Ocean Colour Remote Sensing around Fiji, some

news!

« Two Reef to Ridge projects »

Cécile Dupouy, Jérôme Lefèvre, IRD Nouméa

Awnesh Singh, PaCE-SD, USP, Fiji

Timoci Koliyavu, Andra Whiteside (PHDs) PaCE-SD

Rémi Andreoli, Didier Lille, Bluecham

GIS-RS 2019, ITC, USP, Fiji 1

estimate CO2 sink by phytoplankton in the ocean/coasts

distinguish the signals of Chla and other sources as CDOM

distinguish phytoplankton fonctional types

Seawifs chla in summer

2

Log Rrs440nm (λ)/ Rrs

550nm

30% !

GIS-RS 2019, ITC, USP, Fiji

The Pacific ocean a coloured (productive) area

Absorption

Phytoplancton

absorbe la lumière

bleue

Eau absorbe

la lumière

rouge

Absorption

Phytoplancton

absorbe la lumière

bleue

Eau absorbe

la lumière

rouge

Rétrodiffusion

Lumière bleue rétrodiffusée

efficacement

Rétrodiffusion

Lumière bleue rétrodiffusée

efficacement

Backscattering Absorption (Chl + CDOM)

Sate

llite

Ch

la

GIS-RS 2019, ITC, USP, Fiji 3

Sentinel 3 MODIS turbidity map

Map of turbidity as calculated from MODIS after the tropical storm Ex-Finna (December 2011). (Bluecham SAS.)

Map of Chla as calculated by OC3 (JAXA)

Ridge to Reef program in New Caledonia

MODIS VALHYBIO

What about CDOM ?

• Studies of CDOM and DOC are scarce in tropical environments

• CDOM (Chromophoric Dissolved Organic Matter) is an optically active component as particles…as it absorbs blue light

• Great tracers for anthropogenic pressures systems and major reservoirs of reactive carbon in aquatic systems (attracts pollutants, metals…)

• not necessarily linked to Chlorophyll a, Suspended matter, Nutrients…

GIS-RS 2019, ITC, USP, Fiji 4

Materials and methods

East coast of New Caledonia: the Caliope cruises: 2011, 2014, 2016

GIS-RS 2019, ITC, USP, Fiji 5

Optical measurements from ALIS in the Eastern lagoon ofNew Caledonia.

LwccaCDOM

CDOM and FDOM laboratory measurements at IRD Noumea

FDOM Spectrofluorimeter

GIS-RS 2019, ITC, USP, Fiji 6

East coast of New Caledonia: the Caliope cruises: 2011, 2014, 2016

CAL01-2011 CAL02-2014 CAL03-2016

Cold plumes into the lagoon either from open ocean waters (cool season salted at CAL01) or from freshwater runoffs (rivers as at CAL02 and CAL03) CDOM (warm season)

CD

OM

(m

-1)

Favareto et al., 2018; Martias et al., 2018; Dupouy et al., in press, Frontiers

CDOM traces impact of freshwater runoffs in the Eastern lagoon during warm and rainy season

CDOM maps

CAL01-2011 CAL02-2014 CAL03-2016

CDOM counts !

MODIS imagery : plumes around Fiji

GIS-RS 2019, ITC, USP, Fiji 8

From MODIS-DB IRD NoumeaJérôme Lefèvre

•MODIS Adg, CDOM+detritus (m-1)•MODIS Chla (mg.m-3)•MODIS backscattering bb (m-1)•MODIS Turbidity (g.m-3)

GIS-RS 2019, ITC, USP, Fiji 9

Laucala BayLaucala Bay

MODIS imagery of South Fiji plumes

•Determine temporal variability of CDOM•Link to environmental parameters

Determination of the impact of watershed on lagoons(anthropogenic impacts of lands?)

Origin of the plumes : the Laucala Bay ?

GIS-RS 2019, ITC, USP, Fiji 10

Receives land water inputs from• Town• Sewage• Processing plant… Lagoon responses ?

4 cruises in Laucala Bay3 (Martias, 2015 and 2016)1 (Koliyavu 2017)

Rewa

Laucala Bay under influences of rivers?

GIS-RS 2019, ITC, USP, Fiji 11

• Laucala Bay stations sampled

Rewa

Material and methods: sea cruisesLaucala Bay

GIS-RS 2019, ITC, USP, Fiji 12

Temperature (°C)

GIS-RS 2019, ITC, USP, Fiji 13

Rewa Rewa

CDOM

Optical impact of rivers Dec 2017

See further in Koliyavu, in prep.CDOM counts !

Next: SOKOWASA CRUISE October 2020

GIS-RS 2019, ITC, USP, Fiji 14What about CDOM ?

2 Mini-Fluos (CDOM and FDOM)

GIS-RS 2019, ITC, USP, Fiji 15

FIGURE 3 | Glider-compatible MiniFluo. (a) Picture of the complete MiniFluo: anodized aluminum for the upper

part and copper cylinder for the bottom part; (b) Diagram of the MiniFluo. Difference with Figure 2 is the

electronic circuits placed underneath the photodiodes; (c) Optical cap with the quartz prisms placed at the

center. The two channels for the through flow are also visible. (d) Optical cap (view from above); (e) MiniFluo

installation on the SeaExplorer glider scientific payload; (f) MiniFluo installed with its optical cap.

GIS-RS 2019, ITC, USP, Fiji 16

Mini-Fluos CDOM fluorescence

next: ………..work will go on

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IRD fellowship 3-y2019-2022Learn about variability at week, month,seasonal and interannual scales of plumesaround Fiji from MODIS data Chla, CDOM,turbidity …phytoplankton functional type ?What if a Trichodesmium bloom is triggered there ?

Roudault Gildas, LEMAR

Dupouy et al., 2018Biogeosciences

Last: the COMETE project (Fonds Pacifique fund)

• The objective of the project is to organize a seminar dedicated to ocean colour use possibilities in Pacific Islands

• to create a network and research collaborations between PACE-SD (University of South Pacific) and IRD (New Caledonia and French Polynesia

• Increase capacities of Pacific countries to observe and understand biogeochemical processes around tropical coral islands with ocean colour satellite imagery

• Join us!

GIS-RS 2019, ITC, USP, Fiji 18