Joaquim I. Goes and Helga Gomes Bigelow Laboratory for Ocean Sciences

Increasing productivity in the Arabian Sea linked to shrinking snow caps – How

satellites helped connect the dots

Prasad ThoppilNaval Research Laboratory, Stennis Space Centre

John FasulloPAOS, Univ. of Colorado, CO, USA

Jan 2002

Sept 2002

Nitrate fields generated using MODIS Terra Chl a

and SST

Goes et al., EOS (2004)

Estimating Nitrate In The World’s Oceans and its utility to study environmental regulation of

nitrate based new production in the Arabian Sea

ARABIAN SEA WIND FIELDS

Development and intensity regulated by thermal gradient between land and sea

Sea surface winds reverse direction seasonally

Winds responsible for convective mixing during winter monsoon and coastal upwelling during summer monsoon

Schematic showing snow cover extent and wind direction superimposed on an ocean color chlorophyll image for the northeast monsoon season (Nov-

Feb).

LOW

HIGH

0.1 0.5 1.0 2.0 5.0 10.0 20.0

WINTER MONSOON

DEC 2001 JAN 2002 FEB 2002

MAR 2002 APR 2002 MAY 2002

NITRATE INPUTS IN THE ARABIAN SEA DUE TO WINTER CONVECTIVE MIXING DURING NORTHEAST MONSOON

Schematic showing the reversal in wind direction during the southwest monsoon (Jun-Sept), superimposed on satellite derived chlorophyll fields

LOW

HIGH

0.1 0.5 1.0 2.0 5.0 10.0 20.0

SUMMER MONSOON

JUNE 2002 JULY 2002 AUG 2002

SEPT 2002 OCT 2002 NOV 2002

5 10 15 20 25 30 35

NITRATE INPUT DUE TO UPWELLING DURING THE SOUTHWEST MONSOON

Nitrate (m)

INTERANNUAL CHANGES IN SEA SURFACE NITRATE CONCENTRATIONS DURING THE SW MONSOON

5 10 15 20 25 30 35Nitrate (m)

Goes et al. (2005) - Science

COLDER LANDMASS

SEA

SEA

MORE SNOW

WEAKER SW MONSOON WINDS

WEAKER UPWELLING

LESS SNOW

STRONGER SW MONSOON WINDS

STRONGER UPWELLING

WEAKER LAND SEA PRESSURE GRADIENT

STRONGER LAND SEA PRESSURE GRADIENT

LESS PHYTO

MORE PHYTO

WARMER LANDMASS

Schematic showing the response of the Arabian Sea to more and less snow cover

HIGHER ALBEDO

LOWER ALBEDO

-4

-2

0

2

4

1996 1997 1998 1999 2000 2001 2002

ESC

anom

aly

Anomalies (departures from monthly means for period between 1996-2002) of Eurasian Snow Cover (x106 km2). Trend line shown

in bold is 14 point moving average.

YEAR

Annual snow cover trends suggest a marked decrease in snow accumulation north of the Arabian Sea.

May snow cover trends are largely negative all over Eurasia reflecting an earlier and stronger spring melt-off.

NSIDC SNOW COVER TRENDS

Trend line (14 point moving average) showing anomalies (departures from monthly means) of snow cover extent over Southwest Asia and Himalayas-

Tibetan Plateau between 1967 and 2003. Note especially the runaway decline in snow cover extent after 1997.

-8

-4

0

4

8

1967 1971 1975 1979 1983 1987 1991 1995 1999 2003

Sn

ow

Co

ver

Ext

ent

(%)

-8

-4

0

4

8

YEAR

Southwest Asia

Himalayan-Tibetan Plateau

The warming of SW Eurasia echoes the global-land signal, though recent warm anomalies are >50% larger than for the global temperatures.

Eurasian-Land Warming

Left Panel - TMI derived SST in the Arabian Sea showing upwelling and offshore advection of cooler upwelled waters during the SW monsoon (July) of 2003. Arrows indicate wind vectors for the same

month. Right top panel – Interannual variability of Wind Speed and Wind Stress Curl. Right bottom panel – Decrease in SST along the coast of Somalia

YEAR

23

25

27

29

31

1997 1998 1999 2000 2001 2002 2003 2004

SST

(oC)

-12

-6

0

6

12

18

1997 1998 1999 2000 2001 2002 2003 2004

WS

C (

x10-8

N m

-3)

3

6

9

12

15

Win

d S

pee

d (

m s-1

)

Interannual changes in chlorophyll along coast of Somalia since 1997

0

0.4

0.8

1.2

1.6

2

1997 1998 1999 2000 2001 2002 2003 2004

Year

Chlor

ophy

ll (mg

m-3

)

0.0

0.2

0.4

0.6

0.8

1997 1998 1999 2000 2001 2002 2003 2004

Chl

orop

hyll

a (m

g m

-3)

-0.06

-0.01

0.04

0.09

0.14

Zona

l Win

d St

ress

(N m

-2)Chl a

Zonal Wind Stress

Annual trends of satellite derived chlorophyll a and zonal wind stress in the offshore western Arabian Sea.

YEAR

0

0.05

0.1

0.15

0.2

0 8 16 24 32

Eurasian snow cover (x106 km2)

Win

d St

ress

(N

m-2

)

25

27

29

31

0 0.05 0.1 0.15 0.2Wind Stress (N m-2)

SS

T (

oC)

0.0

0.3

0.6

0.9

25 27 29 31SST (oC)

Ch

loro

ph

yll a

(m

g m

-3)

Scatter plots showing the impact of the decline in Eurasian snow on phytoplankton

in the Arabian Sea

Sept. 1997 Sept. 2003

Enhanced eutrophicationSpread of Anoxia?

Enhanced Denitrification?

Fish Mortality

Rainfall

OUTSTANDING SCIENCE QUESTIONS FOR THE ARABIAN SEA

Identify salient coherent climate signals and synthesize these observations into a coherent diagnosis of climate variability

Examine impact on phytoplankton community structure and carbon flux associated with changing strength of the monsoons.

Examine impact on the Arabian Sea’s Oxygen Minimum Zone

Examine impact on Coastal Fisheries

Examine impact on rainfall over Indian subcontinent

“Nothing in the sea falls haphazard; if we cannot predict, it is because we do not know the cause, or how the cause works..."

Henry Bryant Bigelow

ACKNOWLEDGMENT

This work is being sponsored by NASA,

USA