Schematic Surface and Atlantic Circulation Typical Arctic

2012 Changing Arctic Ocean 506E/497E - Lecture 7 - Woodgate

1

Schematic Surface and Atlantic Circulation

Jones, 2001

Typical Arctic profiles

Bottom Water

“the rest”

Western Arctic warmer

ATLANTIC WATER

T>0ºC, deeper than 200m

Tmax and layer below

Higher Salinities

Radionuclide tracers

Eastern Arctic warmer

PACIFIC WATER

High nutrients

Shallow (<200m) Tmax

Comparatively fresh (<33psu)

Mostly only in Western Arctic

MIXED LAYER

Usually thin (no wind stirring)

The “Accent”

of Sea Water - Pacific and

Atlantic Waters

in TS space

- density determined

mostly by salinity at

T < 2 deg C

The temperature and salinity of a bit of water often tells you where it is from

How to form halocline water?

Adapted from Steele and Boyd, 1998

Atlantic water

Surface Water

- cannot form Halocline

water simply by mixing

(Aagaard, 1981)


2

Temp Fresh Salty

ADD

COLD, SALTY

Aagaard et al, 1981

Rudels et al, 1996 Temp Salty

Co

nve

ct

ADD

COLD, FRESH

~ 50m

~ 100m

~ 50m

~ 100m

ADVECTIVE HC

CONVECTIVE HC

Steele and Boyd, 1998 – source of halocline water differs (advective or convective)

Woodgate et al, 2001 – temperature of halocline water differs

(convective must be at freezing temperature, advective may or may not be at freezing)

Halocline formation

Woodgate etal, 2001

Retreat of the Cold

Halocline (Steele and Boyd, 1998)

In 1995, only Makarov

has a cold halocline

Use salinity in 40-60m

band as an indicator

Hi S = NO CHL

Lo S = CHL

Retreat of the Cold Halocline (Steele and Boyd, 1998)

Injection point of freshwater

(Russian Rivers) has changed

Backed up by chemical data,

Ekwurzel et al., 2001

Guay et al., 2001

PREVIOUS – RW into Eurasian Basin – CHL in Eurasian Basin

1995 – RW along shelf instead – no CHL in Eurasian Basin


3

The (partial) return of

the Cold Halocline (Boyd et al, 2002)

Consider (upper 80m) S over Lomo Ridge

- 1995 ~ 34 psu – no CHL

- 1997 ~ 33.55 psu

- 1999 ~ 33 psu

- 2000 ~ 33.3 psu – CHL returning

What could be causing this??

So far, this is EASTERN Arctic story,

what about the Western Arctic

Western versus Eastern Arctic Halocline

EASTERN ARCTIC (ATLANTIC) HALOCLINE

- less salinity range

- saltier at surface

- sharper bend in TS space

Adapted from Steele and Boyd 1998

BSW – Bering Sea Water

UHW – Upper Halocline Water

LHW – Lower Halocline Water

AW – Atlantic Water

DW – Deep Water

WESTERN ARCTIC

(PACIFIC) HALOCLINE

- greater salinity range

- fresher at surface

- general Tmax above Tmin

- very varied

- (rich in nutrients)

Western versus Eastern Arctic Halocline Image from Steele and Boyd 1998

BSW – Bering Sea Water

UHW – Upper Halocline Water

LHW – Lower Halocline Water

AW – Atlantic Water

DW – Deep Water

European Speak: e.g. Manley et al, 1992

Polar Water T: < 0 deg C and S: <34.4 psu

Arctic Surface Water T: < 0 deg C and S: 34.4-34.9 psu

Atlantic Intermediate Water T: 0-3 deg C and S: 34.4-34.9 psu

Atlantic Water T: > 3 deg C and S: > 34.9 psu

Polar Water

Arctic

Surface

Water

Arctic Intermediate

Water A

tla

nti

c W

ate

r


4

JGR, 2004

ACW=Alaskan Coastal Water

sBSW = summer Bering Sea Water

Generic Pacific Water

circulation Steele et al, 2004

BUT

- doesn’t always match Fram Strait outflow – is there a better tracer

- how get the Pacific Water off from the Chukchi

- change in pathway with change in Atmospheric state

- shift of Pacific/Atlantic boundary from Lomonosov Ridge

Shift of Pacific/Atlantic Front

- Hi Si and low Ox = Pacific Water

- Pacific Atlantic Front retreated from Lomo

Ridge to Mendeleev Ridge by 1993

JGR, 1996

PW - Low Oxygen

NPEO

SWYD

DISSOLVED OXYGEN

- High at surface (ventilated from atmosphere)

- Low = OLD water (long time since at surface)

or

= Evidence of high biological activity

THUS – Pacific Water has LOW Dissolved Oxygen Pacific

Wate

r

Falkner et al, 2005 DSR

AW

PW


5

PW - Hi Nutrients SILICATE, NITRATE, PHOSPHATE

- High from source in Pacific

BUT – not conservative

Try to create a “tracer” that is conservative “Quasi-conservative Tracer”

“NO” and “PO” – Broecker, 1974

- cope with growth and decay

NO = 9 NO3 + O2

PO = 135 PO4 + O2

N:P ratios

NO:PO ratios

N* (N star) – Gruber and Sarmiento, 1997

- indicates nitrogen fixation and denitrification

N* = 0.87 [N – 16 P + 2.9 µmol kg-1]

(CH20)106(NH)16(H3PO4) + 138 O2 = 106 CO2 + 122 H2O + 16 HNO3 + H3PO4

Biogenic matter + oxygen = Carbon Dioxide + Water + NUTRIENTS

Fixing of nutrients and Carbon

to make biogenic matter

Decay of biogenic matter

using up Oxygen, forming nutrients

Redfield-Ketchum-Richards Model (Redfield et al, 1963)

PW versus AW in N:P space NITRATE:PHOSPHATE

RELATIONSHIP

different in AW and PW = For a Nitrate value, PW have more Phosphate

= Slope set by Redfield

= Exact lines may change NO3(pw) = 14.828 x PO4(pw) – 12.16 (Falck, 2001)

BUT work out % influence of PW and AW

(..but certainly no better than 10%

.... assumes ice melt, P and runoff same as AW

.... denitrification .. and other such processes) PW

AW

% PW in upper 30m

Jones, Anderson and Swift, GRL, 1998

Distribution of Atlantic and Pacific waters in the

upper Arctic Ocean: Implications for circulation

Shift of Pacific/Atlantic Front

- use TS and chemistry to show Pacific

Atlantic Front retreated from Lomo Ridge

to Mendeleev Ridge by 1993

JGR, 1996 JGR, 2005

Historic Russian Data

- silicate profiles in central Makarov

- Si max disappears in late 1980s

Near-Surface Temperature Maximum

29th Aug 2006

75N, 150W

Temperature above freezing (deg C)

Formed by local solar input

Can be trapped below surface ice melt

Heat may be removed in winter

Jackson et al, 2010, JGR


6

JGR 2008 Beaufort Gyre

Freshwater Storage Proshutinsky et al, 2009, JGR

1950s to1980s Climatology

- line = 50m salinity

- colors = freshwater relative to 34.8psu

Influenced by

- Ekman Pumping (largest)

- also sea ice melt/formation

and mixing

DSR 2010

- Top 500m Jul-Sep data

- Find FW above 34 psu

isohaline (Sref=35psu)

- Objective mapping

1992-1999 data 2006-2008 data

(2006-2008)

minus

(1992-1999)

Increase of 8400±2000 km3

between these periods

This is 20% of BG storage,

& comparable to annual

Arctic FW export

Bering Strait ~ 2500 km3/yr

Causes?

- Increased river water off shelves

- Regionally, also ice melt

- Speculate = less export of FW to

the North Atlantic

Glaciers = small

Rivers = 1 paper saying increase,

rest small,

Bstrait = no trend .. maybe

Satellite evidence of wind-driven spin up

Nature GeoSci, 2012

SSH Trend

in SSH

Trend in

wind stress

curl

Documents

Schematic Surface and Atlantic Circulation Typical Arctic