Changing productivity in the Arabian Sea linked to shrinking snow

Changing productivity in the Arabian Sea
linked to shrinking snow caps – How
satellites helped connect the dots
Joaquim I. Goes and Helga Gomes
Bigelow Laboratory for Ocean Sciences
Prasad Thoppil
Naval Research Laboratory, Stennis Space Centre
Prabhu Matondkar and Sushma Parab
National Institute of Oceanography
Adnan Al Azri
Sultan Qaboos University
ACKNOWLEDGEMENTS
Dr. Satish Shetye, Director, NIO, Goa for supporting this
work.
Dr. Raleigh Hood and Dr. Wajih Naqvi and the SIBER
committee for the opportunity to attend the workshop.
Dr. Sayed Ahmed for facilitating the collaboration with
SQU.
Dr Karl Banse, Dr. Jerry Wiggert and Special Issues of
Arabian JGOFS
NASA, NSF - USA and SAC - India
Jan 2002
Estimating Nitrate In The World’s Oceans and its
utility to study environmental regulation of
Sept 2002 in the Arabian Sea
nitrate based new production
Nitrate fields generated
using MODIS Terra Chl a
and SST
Goes et al., EOS (2004)
ARABIAN SEA WIND FIELDS
Sea surface winds
reverse direction
seasonally
Development and
intensity regulated
by thermal gradient
between land and
sea
Winds responsible
for convective
mixing during winter
monsoon and
coastal upwelling
during summer
monsoon
WINTER MONSOON
HIGH
LOW
0.1
0.5
1.0
2.0
5.0
10.0
20.0
Schematic showing snow cover extent and wind direction superimposed
on an ocean color chlorophyll image for the northeast monsoon season
(Nov-Feb).
DEC 2001
MAR 2002
JAN 2002
APR 2002
FEB 2002
MAY 2002
Nitrate (μM)
NITRATE INPUTS IN THE ARABIAN SEA DUE TO WINTER
CONVECTIVE MIXING DURING NORTHEAST MONSOON
SUMMER MONSOON
LOW
HIGH
0.1
0.5
1.0
2.0
5.0
10.0
20.0
Schematic showing the reversal in wind direction during the southwest
monsoon (Jun-Sept), superimposed on satellite derived chlorophyll fields
JUNE 2002
JULY 2002
SEPT 2002
5
10
AUG 2002
OCT 2002
15
20
NOV 2002
25
30
35
Nitrate (μΜ)
NITRATE INPUT DUE TO UPWELLING DURING THE
SOUTHWEST MONSOON
Satellite Nitrate (μM)
16
12
8
r2 = 0.904
n=41
4
0
0
4
8
12
16
Shipboard Nitrate (μM)
Comparison between shipboard and satellite derived
sea surface nitrate concentrations in the Arabian Sea
5
10
15
20
25
30
35
Nitrate (μM)
INTERANNUAL CHANGES IN SEA SURFACE NITRATE
CONCENTRATIONS DURING THE SW MONSOON
HIGHER
ALBEDO
LOWER
ALBEDO
STRONGER LAND SEA PRESSURE GRADIENT
LESS SNOW
MORE SNOW
WEAKER LAND SEA PRESSURE GRADIENT
STRONGER SW MONSOON WINDS
LESS
PHYTO
WEAKER SW MONSOON WINDS
SEA
SEA
WEAKER
UPWELLING
WARMER
LANDMASS
COLDER
LANDMASS
Schematic showing the SW Monsoon response of the
Arabian Sea to snow cover
ESC anomaly
4
2
0
-2
-4
1996
1997
1998
1999
2000
2001
2002
YEAR
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.
NSIDC SNOW COVER TRENDS
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.
Snow Cover Extent (%)
8
8
4
4
0
0
-4
-4
Southwest Asia
Himalayan-Tibetan Plateau
-8
-8
1967 1971 1975 1979 1983 1987 1991 1995 1999 2003
YEAR
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.
Eurasian-Land Warming
The warming of SW Eurasia mirrors the global-land
signal, but recent warm anomalies are >50% larger than
for the global temperatures.
WSC (x10-8 N m-3)
12
12
6
9
0
6
-6
-12
1997
Wind Speed (m s-1)
15
18
3
1998
1999
1998
1999
2000
2001
2002
2003
2004
S S T (o C )
31
29
27
25
23
1997
2000
2001
2002
2003
2004
YEAR
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
C h lo r o p h y ll ( m g m-3 )
2
1.6
1.2
0.8
0.4
0
1997
1998
1999
2000
2001
2002
2003
Year
Interannual changes in chlorophyll along
coast of Somalia since 1997
2004
0.8
Chl a
Zonal Wind Stress
0.09
0.6
0.04
0.4
0.2
-0.01
0.0
-0.06
1997
1998
1999
2000
2001
2002
2003
2004
YEAR
Annual trends of satellite derived chlorophyll a and
zonal wind stress in the offshore western Arabian Sea.
Z o n a l W in d S t r e s s ( N m -2 )
C h lo r o p h y ll a ( m g m -3 )
0.14
0.15
0.1
0.05
0
0
8
16
24
32
Eurasian snow cover (x106 km2)
C hlorophyll a (mg m-3
0.2
SST (oC)
W ind Str e ss (N m -2 )
0.9
31
29
27
0.6
0.3
0.0
25
0
0.05 0.1 0.15 0.2
Wind Stress (N m-2)
25
27
29
SST (oC)
Scatter plots showing the impact of the
decline in Eurasian snow on phytoplankton
in the Arabian Sea
31
Sept. 1997
Sept. 2003
southwest monsoon growth season of 1997 and 2003
NORTHEAST
MONSOON
LESS
MORESNOW
SNOW
COLDER
AND DRIER
WINDS
WARMER
AND HUMID
WINDS
SEA
SEA
LESS
MORE
PHYTO
PHYTO
STRONGER
WEAKER
CONVECTIVE MIXING
CONVECTIVE MIXING
WARMER
COLDER
LANDMASS
LANDMASS
Relative humidity and Air-temperature for the
northern Arabian Sea (60°E-70°E, 14°N-25°N).
Annual trends of Mixed Layer Depth (XBT, JEDAC, USA) and
net heat flux (NCEP-NCAR) (60-70°E, 14°N-25°N).
Comparisons of observed and model-derived MLD for winter (Jan – Feb),
and model derived Sea Surface Salinity (SSS, psu) during Jan – May for the
60°E-70°E, 14°N-25°N. Model derived fields are obtained from the ECCO-JPL
Kalman Filter Assimilation project.
Chlorophyll a (m g m -3)
1.5
1.3
WAS
1.1
0.9
EAS
0.7
0.5
1996
1998
2000
2002
2004
2006
Year
Winter mean SeaWiFS Chl a averaged over the Eastern
Arabian Sea (EAS, 66°E-70°E, 15°N-24°N) and in the western
Arabian Sea (WAS, 55°E-62°E, 17.5°N-22.5°N).
NEM 1998/1999
NEM 2005/2006
SeaWiFs derived chlorophyll anomaly plots for the winter monsoons of
(A) Nov 2002 to Feb 2003 and (B) Nov 2005 to Feb 2006.
Sea Surface Height Anomalies (SSHA, cm, contours) and
geostrophic current vectors computed from the SSHA for the period
22-25 February 2003 superimposed on a weekly (18-25 February
2003) averaged SeaWiFS chlorophyll a image.
Dissolved Oxygen (ml)
0
2
4
6
8
0
0
1
2
3
4
0
10
50
Depth (m)
20
30
100
40
50
150
60
200
70
Dec-04
Jan-05
80
Dec-05
Feb-05
90
250
Jan-06
Feb-06
100
St. 10
St. 13
St. 7
St. 1
St. 3
300
Gulf of Oman
Eastern Arabian Sea
5
OMZ
0.1
0.5
1.0
2.0
5.0
Eddies and the OMZ
10.0
20.0
Eddy kinetic energy for the region off the coast of Oman
for the period from 2001 to 2006.
Eddy kinetic energy for the region off the coast of Oman
for the period from 2001 to 2006.
1.8
Gulf of Oman
1.4
1
0.6
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
Area averaged chlorophyll for the Gulf of Oman
2007
Are recent changes in the productivity of the Arabian
Sea related to other modes of climate variability?
How will changes in species diversity and biological
productivity impact:
•
Carbon delivery to deeper layers of the Arabian Sea
•
Bacterial processes
•
Denitrification rates
•
The Oxygen Minimum Zone and
•
Coastal Fisheries?
significance of eddies in
the Arabian Sea?
ACKNOWLEDGMENT
This work is being
sponsored by NASA,
USA
“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