distribution and biological properties of oceanic water

New Zealand Journal of Marine and Freshwater Research, 1991, Vol. 25: 21-420028-8330/2501-0021 $2.50/0 © Crown copyright 1991

21

Distribution and biological properties of oceanic water massesaround the South Island, New Zealand

W.F.VINCENT*

C. HOWARD-WILLIAMS

Taupo Research LaboratoryDSIR Marine and FreshwaterDepartment of Scientific and Industrial ResearchP. O. Box 415, Taupo, New Zealand

•Present address: Departement de biologie, UniversityLaval, Quebec G1K 7P4, Canada

P. TLDESLEY

E. BUTLER

CSIRO Marine LaboratoriesP. O. Box 1538, Hobart, Tasmania, Australia

Abstract The distribution of phytoplankton andthe diversity of environmental conditions for theirgrowth around the South Island, New Zealand, wereexamined in May 1989 by way of chlorophyll afluorescence profiling in combination with discretesample analysis of nutrients and particulates, CTD-profiles, and concurrent satellite images of sea surfacetemperature (SST). A composite of 7 overlaid SSTimages from the period of the cruise emphasised thestrong north-south and east-west gradients in theoceanic environment. Water column sampling coupledwith SST imagery was used to examine the frontalstructure in Cook Strait, upwelling along the WestCoast, gradients across the Solander Trough andthrough Foveaux Strait, and oceanographic featuresassociated with the Subtropical Convergence off theEast Coast and over Chatham Rise. A correlationanalysis of the near-surface water properties showedthe zonal relationships between nutrients, nutrientratios, and temperature, but also underscored thestrong local influence of freshwater inputs around theSouth Island coastline. An analysis of the in vivofluorescence data revealed large site-to-site differences

M90066Received 10 December 1990; accepted 8 February 1991

in the fluorescence yield per unit extracted chloro-phyll a. The yield varied systematically with changesin the physical and biological environment across theSubtropical Convergence.

Keywords Chatham Rise; chlorophyll a; CookStrait; fiords; Foveaux Strait; Mernoo Bank; NewZealand; nutrients; phytoplankton; salinity; SouthIsland; Subtropical Convergence; temperature;upwelling

INTRODUCTION

The South Island of New Zealand has a majorinfluence on the physical and chemical properties ofthe ocean which surrounds it, and these properties arein turn likely to have a controlling effect on biologicalprocesses. The coastal waters of this region containareas of strong boundary forcing, wind-inducedupwelling, sharp gradients in mixed-layer depthinduced by river inflows, fronts, gyres, plumes, andmany other features (see Heath 1985) likely to createa diverse range of biological conditions. Additionally,the South Island lies adjacent to a circumglobal front,the Subtropical Convergence (STC). This major frontseparates subtropical water in the north fromsubantarctic water to the south (Heath 1976; Stanton& Ridgway 1988) and is accompanied by strongphysical and nutrient gradients which have majorimplications for planktonic growth.

The dynamic nature of these complex oceano-graphic features through time and space usually makesit very difficult to interpret biological data collectedfrom discrete locations. However, the concurrentapplication of physical and biological profiling in theocean with real-time satellite imagery provides apowerful combination to define adequately the verticaland horizontal structure of the plankton and itsenvironment. This approach has not been used beforein New Zealand, but relatively clear skies in May1989 allowed for a good set of satellite images of seasurface temperature during a cruise designed todescribe the oceanographic diversity around the SouthIsland.

22 New Zealand Journal of Marine and Freshwater Research, 1991, Vol. 25

NEWZEALAND'

•40"S

•50°

Cape Farewell

y f^Clutha River' J Mouth

170°E 175°_J

Fig. 1 Map of the South Island,New Zealand. A, Stations for RVRapuhia Cruise 2027. B, Themajor fronts and currents aroundthe South Island derived from Heath(1985), Barnes (1985), andBowman et al. (1983) in combin-ation with data from the presentcruise.

B D'URVILLE^COOKCURRENT STRAIT

:.-:L::SV.BfRdP/CAL:::--CONVERGENCE "-45°S

^

Vincent et al.—Oceanic water masses around South Island 23

Fig. 2 Composite of seven SST images over the South Island region for the period 18-28 May 1989. The 200 m isobathis marked in this and subsequent images.

In this paper we first examine the generaldistribution of water masses around the South Islandby way of satellite imagery and CTD profiling. Wethen focus on the water column properties andhorizontal gradients at several key locations: the CookStrait front, the West Coast upwelling region, thePuysegur Bank-Solander Trough area at the south-western corner of the South Island, Foveaux Strait,and the Subtropical Convergence across the ChathamRise. Finally, using the pooled data from this diverserange of oceanic environments, we explore thecorrelative relationships between physical, chemical,and biological variables.

METHODS

All profiling was conducted during Cruise 2027 ofRV Rapuhia between 16 and 29 May 1989. Thecruise track encircled the South Island (Fig. 1A) andincluded 7 stations off the west coast, 5 south-west ofthe South Island, 6 through Foveaux Strait (betweenthe South Island and Stewart Island), and 7 across theChatham Rise on the eastern side of the island, aswell as additional stations to sample specificoceanographic features.

For conductivity and temperature profiling, aGuildline Model 8755 Conductivity-Temperature-Depth instrument was used mounted on a rosette


sampler. The thermistor was calibrated immediatelyafter the cruise in a water bath series with a PRTbridge, Automatic Systems Laboratories Model F6,which was calibrated to the triple point of water.Samples for conductivity-salinity calibration weretaken during the cruise from regions of the watercolumn with stable temperature and salinity properties.These samples were subsequently measured with aGuildline Autosal Laboratory Salinometer, Model8400A. The absolute error in the CTD measurementsis estimated as less than ± 0.025 psu (practical salinityunits), ± 0.010°C (temperature), and + 1 m (depth).

Chlorophyll a fluorescence was profiled with aSeamartek in situ fluorometer protected with a lightshield (Vincent et al. 1989) and mounted opposite theCTD on the rosette sampler. For absolutemeasurements of chlorophyll a, duplicate samplesfrom each depth sampled for nutrients were filteredon to 4.25 cm diameter Whatman GF/F filters andstored frozen. The filters were subsequently groundin 90% acetone in a Teflon tissue grinder, the samplecleared by centrifugation, and then assayed forchlorophyll a by fluorometry before and afteracidification (Strickland & Parsons 1972).

Duplicate samples for paniculate nitrogen andphosphorus analysis were filtered through acid-washed, precombusted Whatman GF/F filters. Thesewere subsequently Kjeldahl-digested and measuredby auto-analyser as described in Vincent etal. (1989).The filtrates were analysed immediately for nutrients(nitrate plus nitrite, ammonium, urea) or were storedfrozen for up to 2 months before analysis (silica,dissolved reactive phosphorus), using the auto-analytical methods detailed in Vincent et al. (1989).

Remote sensing data from the Advanced VeryHigh Resolution Radiometer aboard the NOAA-9and NOAA-11 satellites were received by the CSIROMarine Laboratories facility in Hobart, Tasmania,Australia. Images were there processed to give seasurface temperature (SST) estimates using the methodof McMillin & Crosby (1984) and remapped to astandard cartographic projection (Nilsson & Tildesley1986). The SST values were calibrated using the near-surface (c. 2 m) CTD measurements during the cruise.

RESULTS

General distribution of water massesA satellite mosaic of SST images from throughoutCruise 2027 emphasises the diverse range of watermasses which surround the South Island (Fig. 2; forspecific location names and general oceanographic

16-

14o

f 12

0)

10-

8-

R391

R415

R4t4

34 35

Salinity (psu)

Fig. 3 Temperature-salinity plots for selected stationsthrough the cruise. The curves are derived from the CTD pro -files to 450 m, or to the sea floor if shallower than 450 m.

features see Fig. 1A and IB). The ocean surface was2-8° colder off the east coast relative to the westcoast. Warm waters (>16°C, coloured red) of theSubtropical Zone occurred to the west and north,with a band of cooler water (coloured yellow, 13.5-14.5°C) suggestive of upwelling along the Westlandcoast. From Fiordland southwards there was a gradualtransition across the Subtropical Convergence (STC)into the cold (9°C) waters of the Subantarctic Zone.This frontal transition was diffuse to the west andsouth-west of (he South Island, but was sharply definedalong the south-eastern edge of the continental shelf.The STC lay parallel to the south-east coast of theSouth Island, and then turned eastwards at about44°S, along the southern flank of the Chatham Rise.A band of cooler water extended northwards throughthe Mernoo Saddle, a depression west of MernooBank (Fig. 1A). Large eddies and areas of diffusemixing lay to the north and east of Mernoo Saddle.The cool Southland Current water (green, 12-13°C)was confined to the shelf between the STC (calledthe Southland Front in this region, Fig. IB) and the


east coast, and continued northwards ultimately intoCook Strait.

The broad range of oceanic waters around theSouth Island is further indicated by the temperature-salinity plots for a selection of profiles throughout thecruise (Fig. 3). The plots show a gradation from cold,low-salinity subanlarctic profiles (e.g., R414) to warm,high-salinity subtropical profiles (e.g., R388). Thedeep water T-S properties for all of the stations (withthe exception of the Cook Strait profile, R387) layalong a straight line given by:

Temperature = -236 + 7.1 salinity.

The surface water sections of the T-S plotsdemonstrated a variety of shapes, but in regions offreshwater influence (e.g., Stations R415 and R416off the Clutha River; R400 off Doubtful Sound) thecurves were almost horizontal, indicating the largedilution effect on salinity, but minimal influence ontemperature.

Cook Strait frontThe satellite image of Cook Strait (Fig. 4) showedthat a sharp interface between warm seas to the northand the cold Southland Current water was positioneddown the centre of the Strait, midway between thetwo islands (Fig. 4). The cooler southern waterextended up to the middle of the Narrows. Further tothe north in the Taranaki Bight region there wereirregularly defined eddies where relatively cool(14°C, yellow on Fig. 4) west coast water appearedto be mixing with warmer northern subtropicalwater.

Water column profiles from Cook Strait alsorevealed large vertical gradients in many properties.Station R387 was located within the Narrows on thenorthern side of the front (Fig. 1). The CTD profiles

revealed at least six discrete strata each separated bypycnoclines of varying steepness (Fig. 5C). Warmesttemperatures occurred in the uppermost layer, but asubsurface maximum in salinity occurred at about140 m (Fig. 5B). In vivo fluorescence (Fig. 5C) andchlorophyll a concentrations (Fig. 5A) rose sharplyto a maxi-mum at about 25 m depth, then graduallydeclined to low background values at 100 m. Nitrate(Fig. 5A) and DRP (not shown) rose with depthdown the water column, with the sharpest rise beneath100 m. Even the surface waters, however, were richin nitrate and other nutrients (Table 1). Theconcentration of ammonium and urea, as at all otherstations except in Foveaux Strait (see below),remained at or below our analytical limit of 0.05mmol m~3. The paniculate N:P ratios were highthroughout the water column and indicative of surplusnitrogen relative to phytoplankton growthrequirements.

West coast upwelling

The SST images showed a band of cold waterextended along much of the western coastline of theSouth Island during the period of the cruise (Fig. 2,4,and 6). The coldest temperatures (< 13°C, blue inFig. 6) were in the inshore waters immediatelyadjacent to the coast. The outer region of this bandwas 1-2°C warmer and it was irregularly shaped intoa series of breaking wave-like plumes. One of thelargest of these extended about 40 km out from thecoastline off Abut Head. A series of profiles wereobtained near the centre of this feature (at 43°S,170°E) 12 h after the SST image in Fig. 6. The CTDprofiles (Fig. 7B) showed that the 15°C surfacetemperature was associated with a mixed layer ofreduced salinity that extended to about 30 m depth.

Table 1 Near-surface water piroperties at Cook Strait Station R387, and at stations off the West Coast of the SouthIsland. All samples were at 10 m (except R400, 5 m), 16-21 May 1989. All concentrations are in mmol m"3 unlessotherwise noted. The ratios are molar.

Station

R387R388R389R390R391R392R393R400

Temperature(°C)

15.4115.7215.1914.6014.4914.9414.5614.17

Salinity(psu)

34.9234.8534.6134.6234.3134.6834.0934.28

NO3

3.20.00.42.81.50.90.70.4

Nutrients

DRP

0.410.110.170.250.260.160.200.18

N:P

7.90.02.3

11.05.75.93.32.2

Si

2.91.31.82.51.91.62.12.2

N

0.910.780.761.010.970.921.071.11

Particulates

P

0.050.050.050.140.080.060.060.06

N:P

18.215.615.27.2

12.115.317.818.5

Chi. a(mg nr3)

0.300.290.430.410.710.700.530.52


? i.a 1.1

i NOAAl l 3337CSIRO^MARINE LABS 8409]

19MAY89 0248Z HBT SST LC|

Fig. 4 SST image for the CookStrait-Taranaki Bight region, 19May 1989.

Chlorophyll a (Fig. 7A) peaked midway down thissurface layer and overlaid a region of rapidlyincreasing density (Fig. 7C) and nitrate concentra-tion (Fig. 7A). Even in the near-surface waters,however, nitrate concentrations were at or above1 mmol N m~3.

A larger but similarly shaped plume can be seenin the SST image in Fig. 4 centred at about 41.5°S,171.5°E. It extended about 70 km northwards fromthe Buller River into the Karamea Bight, and pointedin the opposite direction to that off Abut Head,suggesting the different directions of alongshore flow

B Temperature (°C)13 14 15 16

100 -

200 -

30034.6 34.7 34.8 34.9 35.0

Salinity (psu)

C _

0

100 -

200 -

300

-Sigma-t (kg rrf )26

0.05 0.10.15 0.2 0.25 0.3

D Chlorophyll a (mg rrT3)

Fig. 5 Water column properties at Station R387 in The Narrows, Cook Strait, 16 May 1989.

20 30 40 50

— Fluorescence


Fig. 6 SST image for the WestCoast region, 18 May 1989.

at these two widely separated (c. 200 km) locations.The same feature is discernible, but less sharplydefined, in the SST image taken one day earlier(Fig. 6). Our water column sampling in KarameaBight was c. 12 h before the Fig. 6 image, and threeof our stations are likely to have been within the

plume at various distances from the Buller Rivermouth: Station R388 (75 km), R389 (17 km), andR390 (7 km). The CTD-F profiles at Station R388revealed a vertical structure similar to that observedin the plume off Abut Head. A surface layer of coollow-salinity water extended to about 20 m depth and

A • Nitrate (mmol nrf3)

0 2 4 6 8

B — Temperature (°C)

1000.0 0.2 0.4 0.6 0.8

• Chlorophyll a (mg rrf3)

13n 14 150

20

40

60

80

100

-

-

34

1 \ii

i^

i

vA

.6 34.8 35.0

- Salinity (psu)

iii3 I

35.2

16

C Sigma-t (kg m""3)

25.8 26.0 26.2

0 20 40 60 80

Fluorescence

Fig. 7 Water column properties in the plume off Abut Head, Station R392, 18 May 1989.


Fig- 8 Water column propertiesin the plume off the Buller River,Station R388,17 May 1989.

Temperature (°C)

14 15 16

B Sigma-t(kg m 3)

34.8 34.9 35.0 35.1 35.2

Salinity (psu)

10 15 20 25 30 35 40 45

Fluorescence

overlaid a region of increasing salinity and temperature(Fig. 8). Both variables rose to well-defined maximaat around 50 m. The salinity values fell to a secondaryminimum at 60 m, with a third minimum in the well-mixed band of water at the base of the water column.The sigma-t profile was relatively flat to 50 m,suggesting that the temperature and salinity structureabove that depth could be readily disrupted by mixing.As recorded in all of the west coast profiles duringthis cruise, maximum chlorophyll a concentrationsoccurred well below the surface with a substantialdecline in biomass at and below the region of steeplyrising sigma-t. The fluorescence profile had a numberof sharp decreases (22,45, and 55 m), each one ofwhich corresponded to a depth of rapidly changingtemperature and salinity. Nitrate was depleted in thesurface layer to below detection (< 0.05 mmol nr3),but increased in parallel with sigma-t below thislayer.

At stations closer to shore (Fig. 9) there was amarked decrease in surface salinity and a shoaling ofthe upper "mixed layer" from 50 m at Station R388,to 20 m at Station R389, to 5 m at Station R390. Thisreduction in mixed-layer depth was accompanied bya pronounced upward tilting of the NO3, temperature,and salinity isopleths (Fig. 9). There was a rise inchlorophyll a concentration in the surface waters buta decline at lower depths, moving inshore fromStations R388 to R389.

South-western transects

Two transects were sampled to examine the north-south gradient in oceanographic properties off thesouth-western corner of the South Island. The firsttransect extended from Puysegur Bank (Station R401,west of Puysegur Point, Fig. 1A) across the SolanderTrough (R404) to Snares Island (R405), and thesecond from Snares Island along the eastern edge ofthe Solander Trough to the western entrance ofFoveaux Strait (Stations R405-R408).

The SST image on the date that the first transectbegan indicated a gradual transition towards coolerwater from Puysegur Bank southwards (Fig. 10). The1-2°C change in temperature over the 230 km distancebetween Stations R401 and R405 was accompaniedby less than 0.1 psu change in salinity but large shiftsin nutrient and paniculate concentrations (Table 2).In both transects the highest levels of chlorophyll a,paniculate N and P, and the lowest NO3 and DRPlevels were recorded in the northernmost stations.The highest paniculate concentrations in the firsttransect were at Station R402 off the southern side ofthe Puysegur Bank, and were accompanied by amarked depletion of NO3, DRP, and Si. The dissolvedreactive N:P ratio increased with distance south inboth transects. The paniculate N:P ratio variedirregularly over the transects but was usually wellabove the reactive nutrient ratio, and always near orabove the Redfield ratio of 15.5:1.


R390 R389Station no.

R388 R390 R389I

50-

100-

150-

. .16- —

A ; • • . • ; . • . • ; • • • • • . • • • • . • ; • • .

c ••.•••.•••.•••.•••.•••.

50-

1 0 0 -

1 5 0 -

Distance from shore (km)Fig. 9 Temperature (A, in °C), salinity (B, in psu), nitrate (C, in mmol nr 3) and chlorophyll a (D, in mg m~"3) sectionsthrough the plume off the Buller River, 17 May 1989.

Foveaux Strait slightly cooler and less saline water at Station R413The temperature and salinity transects through in the east, consistent with the pattern suggested byFoveaux Strait (Table 3) showed a transition from the SST images (Fig. 2 and 10). The east-westwarm, saline water at Station R408 in the west to gradients within Foveaux Strait were relatively weak


Fig. 10 Composite of 2 SSTimages for the southern SouthIsland region, 21 May 1989.

in all properties, except for nitrate which doubled inconcentration between Stations R412 and R413.Paniculate N varied from 0.4 to 0.9 mmol m~3 with noconsistent trend through the Strait. The paniculateN:P ratios were at or above the Redfield ratio of15.5:1, with the exception of Stations R409 and R410.The latter had a noticeably lower temperature andsalinity relative to the surrounding waters and anelevated silica content. It was a site closest to theSouth Island coast and may have been influenced by

riverine discharges, particularly from the Aparimaand Oreti Rivers.

The profiling at each of the stations in FoveauxStrait revealed a homogeneous distribution ofproperties indicative of strong vertical mixing. The invivo fluorescence values varied by less than 5%down the water column at each station. However, atmost of the stations (R408-R412) there was a smallrise in ammonium (Fig. 11) and sometimes urea andDRP towards the base of the water column.

Table 2 Near-surface properties of the ocean across the two south-western transects. All samples and measurementswere at 10 m, 21-24 May 1989. All concentrations are in mmol m~3 unless otherwise noted. The ratios are molar. Notethat Station R405 forms the southern end of both transects.

Dissolved nutrients Particulates

Station

R401R402R403R404R405

R408R407R406R405

Temperature(°C)

13.7313.8213.1312.3711.97

12.9813.2212.0411.97

Salinity(psu)

34.8934.8834.9234.8234.77

34.8234.8934.7734.77

NO3

2.80.94.05.16.5

2.63.16.96.5

DRP

0.240.080.410.380.36

0.320.370.610.36

N:P

11.611.69.7

13.317.9

8.18.3

11.417.9

Si

1.40.71.51.71.6

1.11.32.11.6

N

0.580.910.610.500.42

0.900.480.380.42

P

0.030.050.040.030.02

0.050.030.020.02

N:P

18.717.214.916.721.0

17.616.519.621.0

Chi. a(mg rrr3)

0.320.460.420.240.17

0.470.140.220.17


Subtropical versus subantarctic profiles

The SST images (e.g., Fig. 2) emphasised the largedifference in surface temperatures between thesubtropical and subantarctic water masses. The majorcontrasts between waters to the north and south of theSTC is seen by a comparison of profiles from twooffshore, geographically well -separated stations: R414in the subantarctic zone and R422 in the subtropicalzone (Fig. 12). Stratification was weakly establishedin the subantarctic relative to the subtropical profile,with a A sigma-t between 50 and 150 m of < 0.1 kg m~3

at R414 and > 0.3 kg nr 3 at R422. The mixed layerwas slightly shallower at Station R422 (c. 70 m) withsubstantial depletion of nitrate and much higherchlorophyll a concentrations relative to Station R414(mixed-layer depth of 100 m). The in vivofluorescence profiles were relatively homogeneousto 75 m at both stations, indicating strong verticalmixing at these exposed oceanic sites. However, it isalso of interest that the strength of the fluorescencesignal was very similar in the two waters despite theirmarkedly different chlorophyll a content (see below).The completely different T-S signatures of the twoprofiles (Fig. 3), with cool low-salinity water at StationR414 and warm high-salinity water at Station R422underscores the major phy sical contrast between thesetwo oceanic zones.

STC over the Chatham Rise

A satellite image taken on 22 May 1989, 3 daysbefore the transect over Chatham Rise, showed thatthe transition from subantarctic to subtropical wateroccurred across a dynamic irregularly shaped frontalzone (Fig. 13). A plume of cold (11-12°C) water(coloured pale blue) streamed northwards over theMernoo Saddle. Further eastwards over the crest and

* Nitrate {mmol m )

2.5 2.6 2.7

• Ammonium (mmol m~ )

0 0.05 0.10

A Chlorophyll a (mg m

13.0 13.2 13.4

• Temperature (°C)

Fig. 11 Water column profiles at Station R408 at thewestern end of Foveaux Strait, 24 May 1989.

to the north of the rise the temperature fluctuationswere complicated by a number of large circularpatches of water that were 1-2°C warmer than thesurrounding ocean. The largest and also warmestof these was centred at c. 42.3°S, 176.0°E and was

Table 3 Near-surface properties through Foveaux Strait, with comparative data for further west (R401) and east(R414). All samples were at 10 m, 22-25 May 1989. All concentrations are in mmol m"3 unless otherwise noted. Theratios are molar.

Station

R401R408R409R410R411R412R413R414

Temperature(°C)

13.7312.9812.4711.9612.1411.9511.619.50

Salinity(psu)

34.8934.8234.7634.5434.7034.6234.7234.36

NO,

2.82.63.43.33.23.36.1

12.0

Dissolved nutrients

DRP N:P

0.24 11.60.32 8.10.41 8.30.40 8.30.24 13.10.27 12.30.43 14.10.76 15.8

Si

1.41.11.21.51.21.51.82.3

N

0.581.10.640.430.520.520.720.65

Particulates

P

0.030.050.040.040.040.030.040.04

N:P

18.717.616.110.513.016.118.016.3

Chi. a(mg nr3)

0.320.470.380.340.260.290.330.22


Fig. 12 Comparison of sub-antarctic (A, C: Station R414) andsubtropical (B, D: Station R422)water column profiles, 25 and 28May 1989.

A Sigma-t (kg m )26

0

100 -

50010 20 30 40 50 60• Fluorescence

B Sigma-t (kg m )26 27

0

50010 20 30 40 50 60

- Fluorescence

• Nitrate (mmol m )0 5 10 15 20

5000.0 0.2 0.4 0.6 0.8

D • Nitrate (mmol rrf0 5 10 15

0

100

200 i

300 •

400

20

1

I 1 1

1 1

- 3 \• Chlorophyll .a (mg m )

0.0 0.2 0.4 0.6 0.8

• Chlorophyll a (mg m"3)

c. 110 km across. A second patch was centred exactlyover the Mernoo Bank and appeared to be connectedto a stream of warm water moving southward into thefrontal zone. A third circular patch was centred atc. 42.6°S, 174.5°E (Fig. 13, Fig. IB) just north-westof Mernoo Bank.

The cruise transect across Chatham Rise wasbroadly consistent with these SST observations. Thesharpest temperature change was around 44°S, well

south of the crest of the rise (Fig. 14 A). A change insalinity of c. 0.4 psu accompanied this temperaturegradient (Fig. 14B). The circular feature centred overMernoo Bank contained well-mixed, moderatelywarm (c. 13°C), saline (c. 34.72 psu) water and wasbounded to the north and south by cooler, less-salinewater. The mixed layer deepened to c. 100 m overMernoo Bank from < 70 m in adjacent stations (R417and R422). A tongue of high-salinity water (up to


Fig. 13 SST image for theMernoo Saddle-Chatham Riseregion, 23 May 1989. Note theposition of Mernoo Bank at43.5°S,175.5°E demarcated by the 200 misobath.

34.8 psu) extended from the southern side of the riseat about 200 m depth. This water gradually decreasedin salinity, cooled, and deepened as it movedsouthwards. This feature was still well defined 150km from Mernoo Bank, but at c. 200 km (StationR417) was no longer discernible.

The eddy-like circular feature over Mernoo Bankcan also be resolved in the nutrient and paniculatedata as a region of slightly higher nitrate and reducedchlorophyll a (Fig. 14C and 14D). Highest chlorophylla concentrations were recorded well south of the riseat Station R419, within the frontal region of mostrapid temperature and salinity change. The core of

elevated chlorophyll a (up to 1.5 mg m 3) lay immed-iately above a tongue of low-salinity subantarcticwater that was at about 60 m depth.

A comparison of nutrients and particulates at 10 mdepth shows the large but irregular variations fromsouth to north in oceanographic properties (Table 4).Silica, nitrate, and DRP were substantially reduced atStation R419 relative to R414 and approachedconcentrations comparable with waters much furtherto the north (Stations R422, R423). Inorganic as wellas paniculate N:P ratios were highest in the southwith an abrupt fall in paniculate N:P at the stations ofhighest chlorophyll a, R419 and R422. Paniculate

Table 4 Distribution of oceanographic properties off the East Coast of the South Island from south to north. Allsamples were at 10 m. 25-28 May 1989. - , no data. All concentrations are in mmol rrr3 unless otherwise noted. Theratios are molar.

Station

R414R417R418R419R420R421R422R423

Temperature(°C)

9.509.739.82

11.7313.0813.0512.7411.85

Salinity(psu)

34.3634.2534.3434.5134.7234.7134.6334.63

NO,

12.012.111.87.25.56.55.46.1

Dissolved nutrients

DRP

0.76__0.55__0.490.55

N:P

15.8——

12.7_—

11.011.1

Si

2.3—_0.9——1.31.0

N

0.650.850.721.150.740.600.771.27

Particulates

P

0.040.050.050.080.050.040.050.09

N:P

16.317.114.413.614.516.915.413.6

Chi. a(mg rrr3)

0.220.240.301.460.510.270.620.88


R417

500

Station no.

R419 R420 R421 R422 R417 R418 R419 R420 R421 R422I I I I

300

Distance (km)

Fig. 14 Temperature (A, in °C), salinity (B, in psu), nitrate (C, in mmol rrr3) and chlorophyll a (D, in mg m"3) sectionsacross the Chatham Rise along longitude 175°E, 25-28 May 1989.

N:P ratios were much higher in the water over MemooBank (Stations R420, R421) than at adjacentstations.

Inshore watersMany of the stations sampled inshore near the east aswell as west coast of the South Island were stronglyinfluenced by freshwater inputs to the sea Althoughthe surface water salinities were rarely diluted below34.0 psu there were major changes in the physicalstructure of the water column, with a surface mixed

layer of 5 m (e.g., Station R390) to 10 m (e.g.,Station R415) overlying a strong pycnocline of risingsalinity. These thin surface inshore layers were slightlycooler than the water beneath, but the temperaturedifference was rarely more than 0.3°C (e.g., off theClutha River, Fig. 15).

Multiple pycnoclines were a feature of many ofthe inshore profiles, for example, at 10 m and 14 m atthe Clutha River offshore station (Fig. 15). Thismultiple layering was especially conspicuous offThompson Sound (Station R393) and Doubtful Sound


Fig. 15 Water column properties A _ Fluorescence; Nitrate (mmol rrf3) Iat Station R416, off the CluthaRiver, 25 May 1989.

0.0 0.2 0.4 0.6 0.8 1.0 1.2

D Chlorophyll a (mg rrf3)

I Temperature ( C)

12 14

5

10

15

20 I-

25 I-

3033.5 34.0 34.5 35.0 35.5

• Salinity (psu)

I%1 1

1 1

1 1

1

(Station R400, Fig. 16) where ihe freshwater outflowswere discharged into a deep water column. A surfacelayer of gradually rising salinity and temperatureoverlaid a sharp pycnocline at 10-20 m depth, with asecond pycnocline at the base of the offshore mixedlayer, at about 90 m. The fluorescence profilesindicated a sharp minimum in chlorophyll aconcentrations at the base of the upper pycnocline.

Nutrient and paniculate concentrations werehighly variable between the inshore stations butchlorophyll a values inshore were often higher thanat adjacent sites further from the coast (Table 5).Silica levels were higher than in surface water offshoreand at deeper inshore depths, reflecting the input ofterriginous nutrients. Some of the dissolved inorganic

N:P ratios in these surface waters were among thelowest recorded during the cruise (e.g., 1.9 at StationR391), but the paniculate N:P ratios were often muchhigher and bore little relationship to the nutrients.

General relationships between properties

Several significant correlative relationships wereobserved between the oceanographic variablesmeasured in this study. Table 6 gives the correlationcoefficients for the surface mixed-layer data presentedin Tables 1-5. Nitrate and DRP, and also their ratio,were significantly and inversely correlated withtemperature reflecting the high nutrient content of thecool subantarctic waters, and the tendency towardsnitrate depletion (to a greater extent than DRP

Table 5 Surface water properties at inshore sites around the South Island, 17-25 May 1989. Samples and measurementswere in the depth range 0-2 m. The number in parentheses is the distance from shore in km. All concentrations are inmmol m~3 unless otherwise noted. The ratios are molar.

Station

R390 (7.8)R391 (5.7)R393 (2.6)R400 (4.4)R415 (15.6)R416 (5.0)

Temperature(°Q

14.40314.34014.57014.16211.16511.365

Salinity(psu)

34.31734.24534.08834.24033.79933.903

NO3

2.70.30.70.45.85.3

Dissolved nutrients

DRP

0.290.160.220.190.460.32

N:P

9.31.93.22.1

12.616.6

Si

2.82.02.42.23.14.0

N

1.181.811.521.131.061.41

Particulates

P

0.160.130.080.070.070.13

N:P

7.313.919.116.115.110.4

Chi. a(mg m"3)

0.320.860.440.460.290.62


• Nitrate (mmol m )

0 2 4 6 8 10 12 14

B —Temperature (°C)

12 14

400 &0.0 0.1 0.2 0.3 0.4 0.5 0.6

. - 3 \

300 -

40035.5

C Sigma-t (kg m 3)

25.5 26.0 26.5Opzr

34.0 34.5 35.0

• Chlorophyll a (mg m"J) Salinity (psu)

Fig. 16 Water column properties at Station R400 off Doubtful Sound, 21 May 1989.

300 -

400

27.0

20 40 60 80 100

— Fluorescence

depletion) in the warmer subtropical waters. Silicadid not show the same effect, but was inverselycorrelated with salinity, indicative of the freshwaterinfluence on both variables. A similar inshore effectshowed up in the inverse correlation betweenpaniculate N and P, and salinity. These elementalpaniculate concentrations were uncorrelated withdissolved nutrients but were correlated directly withchlorophyll a. The paniculate N:P ratios showed norelationship to the dissolved-nutrient ratios, butcorrelated signifi-cantly with the particulate-phosphorus concentrations.

As a further guide to planktonic biomass at eachstation, the total water column content of chlorophyll

a was estimated by trapezoidal integration down tothe depth of background chlorophyll a fluorescence.The integral biomass ranged from 5 to 10 mg Chi. am~2 at the shallow sites (e.g., R409-R412 in FoveauxStrait), to > 50 mg Chi. a m~2 at certain oceanic stations(maximum of 88.2 mg Chi. a nr2 at R419). The inte-gral biomass estimates correlated with the near-surfaceChi. a concentration (but r2 only 0.422), and therewas no significant correlation with any other measuredvariable.

The correlation analysis was subsequentlyrepeated for an offshore subset of the data to determinewhether there were similar relationships betweenvariables for a specific group of deep oceanic stations.

Table 6 Correlation matrix for the oceanographic properties of the surface mixed layer using the data in Tables 1 to 5.T = temperature, S, salinity; PN and PP, paniculate N or P; N, NCyN; P, DRP; Si, silica; IChl. a, integral Chi. a. Onlycorrelations at P < 0.05 are given.

TSNPSiN:PChi. aPNPPPN:PPIChl. a

T

1.00_

-0.87-0.78-

-0.79____-

S

1.00_--0.61_—-0.66-0.41—-

N

1.000.93_0.80____-

P

1.00—0.60___

-

Si

1.00——0.39__-

N:P

1.00____-

Chi. a

1.000.570.52_0.65

PN

1.000.75_-

PP

1.00-0.58

-

PN:PP IChl. a

1.001.00


The data set was restricted to 8 stations 100 km ormore off the east coast of the South Island: R414 andR417-R423. This subset therefore encompassed thestrong gradients across the STC and over ChathamRise, but minimised any coastal and east-west effects.This analysis identified many of the same correlativerelationships as in the overall data set (Table 7).Temperature and salinity were closely correlated witheach other, and inversely with nutrients. There wasan extremely close inverse relationship betweentemperature and DRP (r2 = 0.996) but less preciseinverse correlations with NO3 (r

2 = 0.921), silica(r2 = 0.672), and NO3/DRP ratio (r* = 0.903). Thesalinity effect on silica and particulates was no longersignificant, further supporting the conclusion thatthis was a coastal effect in the full data set (seeabove). In addition to correlations with the other esti-mates of paniculate concentration, Chi. a was signi-ficantly and inversely related to paniculate N:P ratios;at the higher biomass concentrations the seston wasdepleted in N relative to P. Integral Chi. a was muchmore closely correlated with surface concentrationsof this pigment than in the overall data set, and also topaniculate N and P. As with the full analysis, therewas no relationship with nutrients, temperature, orsalinity. None of the descriptors of biologicalparticulates correlated with the physical or chemical-state variables (Table 7).

In vivo chlorophyll a fluorescenceThe in vivo fluorescence profiles through the cruiseprovided an excellent guide to the detailed verticaldistribution of phytoplankton, and at any single stationthere was usually a close relationship betweenfluorescence and chlorophyll a (e.g., r = +0.89 forR414; +0.98 for R419; +0.94 for R388), However,

150

100 -

§ 50 -

Chlorophyll a (mg m °)Fig. 17 In vivo fluorescence (instrument units) againstextracted chlorophyll a concentrations for all stations anddepths.

this relationship was much less precise betweenstations. For example, the least-squares regressioncurve for fluorescence (F) was:F = 12.36 + 152.3 Chi. a for the profile at R414but F = 10.9 + 54.2 Chi. a at R419. For the cruisedata at all depths and stations (n = 188) the correla-tion coefficient was +0.76 (Fig. 17), and for the10 m data in Tables 1-5 the coefficient dropped to+0.56.

To examine whether there was an influence ofsurface bright light on fluorescence yield thefluorescence per unit Chi. a (FQJ a) was calculated

Table 7 Correlation matrix for the oceanographic properties of the surface mixed layer for the Chatham Rise transect(Stations R417-R423), plus Station R414. T, temperature; S, salinity; PN and PP, paniculate Nor P; N, NCyN; P, DRP;Si, silica; ZChl. a, integral Chi. a. Only correlations at P < 0.05 are given.

TSNPSiN:PChi. aPNPPPN:PPiChl. a

T

1.000.96

-0.96-1.00-0.82-0.95____-

S

1.00-0.95-0.93-0.79-0.99____-

N

1.000.990.880.99___

-

P

1.000.860.96__

-

Si

1.00_____-

N:P Chi. a

1.001.000.780.820.730.94

PN

1.000.99_0.85

PP

1.00-0.80

0.89

PN:PP IChl. a

1.001.00


for 0 m and 10 m at each site, and then the 0 m FQ,, a

was divided by the 10 m value. These ratios werethen split into two groups: stations sampled duringdaylight hours and at night. There was no significantdifference between these latter two groups, with thedepth ratios averaging 0.95 (SD = 0.18) in the dayand 1.07 (SD = 0.37) at night. However, the lowestratios were recorded in the daytime data set (minimumof 0.68 at Station R391), suggesting surface inhibitionat certain stations.

The correlation analysis was then extended toexamine the relationship between FChl a at 10 m andthe other oceanographic variables. In the overall cruisedata set there was a significant positive correlationwith nitrate (+0.52), and significant negativecorrelations with Chi. a (-0.51), integral Chi. a (-0.58),and temperature (-0.54). Over the Chatham Risetransect (Stations R414, R417-R423) FQ,, a washighest in the south (maximum of 205 at StationR414), and low in the north (79 at Station R422), andcorrelated strongly with the gradients in otheroceanographic variables across this region. Thecorrelation was positive with NO3 (0.91), DRP (0.92),silica (0.98), nutrient ratios (0.85), and paniculateratios (0.64); it was negative with temperature (-0.84),salinity (-0.84), chlorophyll a (-0.72), paniculatenitrogen (-0.41), paniculate phosphorus (-0.50), andintegral chlorophyll a (-0.80).

DISCUSSION

The temperature, salinity, and surface nutrient datapresented here are broadly consistent with previousstudies at specific sites around the South Island(e.g., Jillett 1969; Heath 1971a, 1971b, 1985; Stanton1971,1976; Bradford 1983; Hawke 1989). However,the combination of these data with near real-timeSST imagery and with fluorescence, paniculate, andnutrient profiling provides a unique overview of thebiological environments which characterise thecoastal and offshore waters of the South Island.

The T-S characteristics plotted in Fig. 3 derive inpart from the zonal position of New Zealand watersin the South Pacific Ocean, and in part from a broadrange of local influences, particularly in the surfacemixed layer. Almost all of the deeper waters followedthe same linear T-S relationship. This tight relationshiprepresents the mixing curve between SubtropicalLower Water (STLW) and Antarctic IntermediateWater (AAIW) (B. R. Stanton, New ZealandOceanographic Institute, unpubl. data). The highsalinity of STLW results from evaporation at the

centre of the subtropical gyre to the north of NewZealand. This water then flows southwards and isdiluted near the surface by the freshwater influencedshelf water, resulting in a subsurface salinitymaximum recorded previously off the west coastbetween l l m and 250 m (Stanton unpubl. data).Subsurface salinity maxima were commonly observedduring the present cruise, for example at 100 m depthoff Doubtful Sound, and at 50 m in Karamea Bight.These features were sometimes accompanied by atemperature maximum at the same depth, furtherreflecting the subtropical origins of this water. AAIWhas a salinity minimum of about 34.44 psu, but offthe west coast this minimum occurs at about 1000 m(Stanton 1971), well below the maximum depth ofsampling in the present study. The tongue ofsubsurface high-salinity water on the east coasttransect extended at least 150 km to the south ofChatham Rise (Fig. 14). This tongue can extend c. 1400km to the Polar Front in other regions, but itssouthward extent is limited by the Chatham Rise inthis area (Heath 1976).

The T-S curve for Cook Strait Station R387(Fig. 3) deviated substantially from the other deepprofiles. Three separate currents come together insouthern Cook Strait (Fig. IB): the D'Urville Currentwhich brings in subtropical water eastwards andsouthwards from the west coast of the North Island,the East Cape current which delivers water flowingsouthwards along the east coast of the North Island,and the Southland current which flows northwardsalong the east coast of the South Island (Heath 1985).This is a region of mixing and complex hydrodynamicexchange, and the unusual T-S plot is probably areflection of these disparate origins.

The sharply defined front in Cook Strait observedin the SST images (Fig. 2 and 4) appears to be avariable feature that is formed by the incursion of thewarm D'Urville Current down the western side of theNorth Island (the Manawatu Coast) into cool, tidallymixed Southland Current and upwelled water insouthern Cook Strait (Bowman et al. 1983; Bradfordet al. 1986). This incursion is probably driven bynortherly winds (Bowman etal. 1983), and the strengthand position of the thermal front is therefore likely tobe highly dependent on recent weather conditions.Unfortunately, no concurrent data are available fromsouth of the front, but the profiling at Station R387revealed a complex vertical structure in all biologicaland environmental variables that was not apparentfrom the surface properties.

The inshore band of cold water extending downthe west coast of the South Island and the upward


tilting of nutrient, temperature, and salinity isopleths(Fig. 9) are consistent with upwelling as describedfor this region by Stanton (1971, 1976). The lowinshore temperatures are unlikely to be the directeffect of cold riverine inflows because these inputsare substantially diluted by mixing with the sea closeto the coast and the difference between river and seatemperatures is not large. In hydrographic surveysaround the Buller and Karannea River mouths, forexample, there is a well-defined effect on the salinityfield, but it is rarely associated with a majortemperature anomaly (Stanton 1972). It is possible,however, that the freshwater inflow contributes to thecooler surface temperatures indirectly by produc-ing a shallower mixed layer that because of itsreduced volume is subject to more rapid cooling byheat exchange with the atmosphere (in winter) andby the input of cold upwelled water. Small patchesof the coldest water in our West Coast SST images(e.g., 12-13°C, blue, Fig. 6) occurred in the immediatevicinity of the mouths of the largest rivers alongthe coast The mean discharges for May 1989 were(see Fig. 1): Buller River, 178 rn3 r 1 ; Grey River, 219m3 s"1; and Whataroa River (discharging at AbutHead), 74 m3 s"1 (Water Resources Survey unpubl.data).

Figures 2,4, and 6 emphasise the highly irregulardistribution of cool inshore temperatures that mayderive from upwelling along the South Island westcoast The plumes which extended up to 75 kmseawards resemble the seaward jets or "squirts"reported in other upwelling environments where theyare an important mechanism of cross-shelf transport(e.g., Kosro & Huyer 1986). These features appear tobe highly transient in the west coast setting, andfrequently associated with specific topographicfeatures (M. Moore, New Zealand OceanographicInstitute, unpubl. data). The sampling of the plumesnorth of the Buller River and off Abut Head showthat they are composed of a relatively shallow layerof low salinity water with considerable variabilityfrom site to site and with depth in their nutrient andbiological paniculate characteristics. The mostextensive area of cold water occurred in the plumethat extended northwards from Cape Foulwind, itsorientation probably dictated by the Wesdand Currentand its size dictated by the huge discharge of theBuller River on this coastline. The shallow mixedlayer which accompanies these extensive offshoreplumes is likely to exert a major influence on thebiological environment A modelling analysis ofmicrobial food chain processes for this region hasshown that the conditions which result from the

combination of upwelling and mixed-layer shoalingcould lead to enhanced growth rates of all com-ponents of the inshore plankton (Kumar et al. inpress).

The waters south of the South Island (Tables 2and 3) contain regions of strong gradients and mixingbetween the cool subantarctic water and warmer,more saline subtropical water. The most saline(34.82 psu) and warmest (12.98°C) conditions inFoveaux Strait were in the west indicating the intru-sion of subtropical water via the current which sweepsaround the south-west South Island and ultimatelybecomes the Southland Current (Fig. IB). The satelliteimagery (Fig. 2 and 10) is consistent with theseobservations, showing a tongue of wanner water(13-14°C; yellow in Fig. 2, red in Fig.10) penetratinginto Foveaux Strait from the west The elevatednutrient concentrations relative to offshore watersalong the west coast, however, imply some mix-ing with subantarctic water as far west as StationR401.

The fluorescence, temperature, and salinityprofiles in Foveaux Strait indicate that these shallowwaters are reasonably well mixed vertically.Ammonium and urea remained at or below our limitsof detection at most stations and depths throughoutthe cruise, but in Foveaux Strait there was ameasurable increase in these highly labile nitrogensubstrates towards the sediments. These bottomgradients imply fast rates of reduced nitrogen releaseby secondary production in the sediments relative torates of diffusion and advection in the overlyingwater column.

The SST images in the Chatham Rise regionshow a surface tongue of cool water penetratingnorthwards through Memoo Gap. This temperaturefeature is consistent with the upwelling of deepSouthland current water moving northwards and risingup over the saddle (Heath 1981) although it maysimply represent the northward advection of coldSouthland Front water at the surface. Reactivephosphorus concentrations up to 0.95 mmol m"3 havebeen previously recorded here, highly suggestive ofupwelling (Bradford & Roberts 1978).

The large circular feature located at 42°S, 176°E(Fig. 2 and 13) frequently appears on SST imagesand appears to be more or less permanently stationedoff the south-east comer of the North Island (Barnes1985). It is an anticyclonic eddy (anticlockwiserotation) believed to be formed by the interactionbetween the East Cape and Southland Currents(Barnes 1985). In our transect over Chatham Rise weidentified another eddy-like feature positioned over


Mernoo Bank. In the CTD sections it appears as athermostad region of homogeneous warm temper-ature and high salinity indicative of its subtropicalorigin. The mixed layer was much deeper than waterto the north and south, with elevated nitrateconcentrations and reduced chlorophyll a levels. Thesefeatures may reflect the short residence time ofphytoplankton within the patch and/or the light-limitation of their growth rates relative to the shallowermixed-layer environment in the ocean to the northand south.

The correlation analysis reported here showedthat there was little relationship between the biologicalparticulates and the physical or chemical variables ineither the overall data set (Table 6) or the ChathamRise subset (Table 7). This is consistent withobservations by Viner & Wilkinson (1988) in theWestern Cook Strait region where there was also nocorrespondence between chlorophyll a and nitrate. Theconcentration of phytoplankton biomass at any onelocation results from a complex balance betweenproduction and loss processes, and it is not un-expected that there is little correlation with specificenvironmental state variables. However, nutrientconcentrations correlated well with the zonalvariations in temperature (Tables 6 and 7) and salinity(Table 7). These data were obtained in autumn whenlight was potentially a limiting factor for algal growth,and this zonal relationship may be less apparent atother times when (or if) much higher phytoplanktonbiomass and nutrient depletion is achieved. BothNO3 and DRP decreased in the subtropical water, butNO3 to a greater extent, giving a strong inversecorrelation between nutrient N:P ratios andtemperature (Tables 6 and 7). This implies anincreasing shift towards N limitation at lowerlatitudes.

In vivo fluorescence profiling is an oceano-graphic technique of widespread use internationally,but has only recently been applied to the seas aroundNew Zealand. In the present study the profilesprovided an immediate and informative guide to thelower depth limit of the phytoplankton and gave adetailed picture of the vertical changes in biomass inrelation to physical and chemical gradients down thewater column. This record was obtained in real timeon board the ship and could therefore be used toselect the appropriate depths for discrete nutrient andpaniculate sampling. Several of the profiles showeda series of pronounced fluorescence discontinuitiesassociated with sharp gradients in temperature and/orsalinity (e.g., Stations R388, R400). The cause ofsuch variations remains unknown but the profiles

suggest abrupt shifts in phytoplankton communitystructure or physiology between adjacent strata.

Although fluorescence correlated well withextracted chlorophyll a down each profile, the exactrelationship between the two variables changedsubstantially between stations, and in the overall dataset chlorophyll a explained only 58% of the variancein fluorescence. This is consistent with the well-known influences of a broad range of biologicalfactors on fluorescence yield (FQJ a) including cellsize (Alpine & Cloern 1985), taxonomic composition(Vincent 1984), and photophysiological processes(Vincent in press).

The large variations in FQJ a across the ChathamRise and its significant correlation with such a largenumber of other variables indicates a systematic effectof the environment on this ratio, but does not allowthe primary causal factors to be identified. It ispossible, for example, that higher chlorophyll aconcentrations (and depleted nutrients) are accom-panied by a shift towards larger-celled phytoplankton;this would account for the reduced F Q J a (e.g., Alpine& Cloern 1985), its significant inverse relationshipwith chlorophyll a concentration, and positiverelationship with nutrients.

The SST imagery obtained during this cruiseprovided a useful overview of the distribution ofwater masses around New Zealand, and given thecorrelation between temperature and NO3, DRP, Si,and N:P ratios, provided a first order guide to thenutritional environment for the phytoplankton.Without vertical sea truth information, however, theapplication of satellite images of sea surfacetemperature as a guide to the planktonic environ-ment, surface colour as a measure of phytoplanktonbiomass, or surface fluorescence as a measure ofproductivity, will be severely limited in New Zealandwaters. Our analyses show that the depth of the mixedlayer containing the phytoplankton varies enormouslywith location, and features such as the west coastplumes and the eddy-like patches near the ChathamRise are associated with large perturbations of theupper water column that are likely to influencestrongly the vertical structure and productivity ofthe plankton. Surface chlorophyll a concentrationwas an imprecise index to the total water columnstanding stock of chlorophyll in the overall data set(r2 = 0.42) but the much better fit in the ChathamRise subset (r2 = 0.88) suggests that specific locationscan be identified within the New Zealand ExclusiveEconomic Zone where satellite imagery of seasurface properties will provide a reliable biologicalindex.


ACKNOWLEDGMENTS

We thank Liana Hrstich and Stu Pickmere for technicalassistance; Janet Bradford, Mike Moore, Ken Grange,Basil Stanton, and Ron Heath for helpful advice anddiscussion throughout all stages of this work; Julie Hall,Anthony Cole, Lynell May, Stu Pickmere, and Rob Davies-Colley for shipboard assistance; the master and crew ofCruise 2027 of RV Rapuhia; Janet Simmiss for word-processing support; and Tangaroa for such a remarkablenumber of cloud-free satellite passes during the cruise.

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