Chemical tracers of shelf derived waters in the Arctic Ocean

Matthew B. AlkirePolar Science Center

Applied Physics LaboratoryUniversity of Washington

NABOS CruiseAug. – Sept. 2013

Some useful chemical tracers

• Salinity• Iodine-129• d18O• O2

• NO3

• NO3:PO4

Carmack et al. (2008)

“Tracers” can help us to visualizeand track changes incirculationof separatewater types

129I @ sfc

Karcher et al (2012)Smith et al. (1998)

1990

129I @ sfc

2004

Karcher et al(2012)

Greenland

EastSiberianSea

LaptevSea

Kara Sea

BarentsSea

ChukchiSea

RUSSIAUSA

Shelf Processes

Carmack & Wassmann (2006)

River runoff

Sea ice

Carbon & nutrient cycling

Modify waters on the shelf

Nutrientcycling

Chemical fingerprints

Steele & Boyd (1998)

brine: negative d18O (16O rich)sea ice: positive d18O (18O rich)

16O16O 16O

16O

16O

18O 18O

18O18O

18O18O 18O

18O

16O

18O

18O

16O

16O16O

16O

sea ice

seawater + brine

(18O:16O)water = 1:1,

(18O:16O) ice = 3:1,

(18O:16O) water ~ 1:2,

Water column

freeze

melt

H218O versus H2

16O

16O > 18O isotopically light

18O > 16O isotopically heavy

Sea-ice melt

Meteoric water(precip., river runoff, glacial melt)

Atlantic water

ice melt

ice formation/brine release

Where would you expect shelf waters to plot on this graph?

Bauch et al.(2009)

Bauch et al.(2009)

Station 87°N, 180 (NPEO 2012)

Advantage of O2 & NO3?

106 CO2 + 16 HNO3 + H3PO4 + 78 H2O = C106H175O42N16P + 150 O2

Alkire et al. (2010)

Can you identify theshelf water signature?

Redfield

Air-sea exchange

denitrification

N2 fixation

Mixing and/or convection?

Station 87°N, 180 (NPEO 2012)

What’s going on here? Canada Basin, 2008

Makarov Basin

Amundsen Basin

NO = (9 x NO3) + O2

A minimum in NO has classically beenused to identify lower halocline water

Jones et al. (2003)

malkire@apl.washington.eduwww.psc.apl.washington.edu

North Pole Environmental Observatory

Questions?

Freshwater in the Arctic

• River runoff• Pacific inflow through

Bering Strait• Precipitation• Glacial melt• Groundwater

Nishino et al. (2013)

Itoh et al. (2007)

Convective or “Fram StraitBranch” halocline water

Advective or “Barents SeaBranch” halocline water

Rudels et al. (2004)

Cyclonic years Anticyclonic years

Yamamoto-Kawai et al. (2005)

How will this picture change in the future?

What makes shelves special?

• River runoff• Sea ice formation

(e.g., polynyas)• Biological production• Organic matter

respiration

• Halocline formation• Mixing• Carbon