Transcript Alaska Science 2006

Climate change research
in the Gulf of Alaska
Russ Hopcroft, Ken Coyle, Tom
Weingartner, Terry Whitledge
Why care?
Late 1960’s
Ecosystem state
+North Pacific 1977 Regime Shift
Summer PDO
?
0
-
1950
a
Cool Phase
1960
1970
1970
Warm Phase
1980
1980
1990
2000
1990
Mid 1970’s
Early 1980’s
Changes catches in a small mesh bottom
trawl in Pavlof Bay, Alaska, through the
regime shift of the mid-1970s.
The currents and water column properties respond to changes
in the Aleutian Low Pressure System and convey physical and
biological climate signals from lower latitudes.
COASTAL GULF OF ALASKA STUDY AREA
• Data over ~3
decades
• GLOBEC 19972004 “Why is this
system so
productive…..”
200km
Climate: Salmon
• NPRB 2005 &
2006
• Long-term?
Annual
cycle
• Surface water
warms
seasonally
• PWS and
Alaska Coastal
Current freshen
over summer &
fall
Chlorophyll a (mg m-3)
April 1, 2003
May 16, 2003
2.5
2.0
Cross-shelf
Average
1.5
1.0
0.5
0.0
Mar Apr May Jun Jul Aug Sep Oct
Primary production starts
on the inner shelf earlier
(0.5 – 1 month) than the
mid- and outer shelf
where it peaks in May
Neocalanus
The success of the
zooplankton that
dominate the
spring is related to
their unique
adaptations to the
production cycles
of the Gulf
Would climate change
lead to a year-round
dominance of small
species (poor fish
food)????
Note that while
Neocalanus may
dominate biomass,
Pseudocalanus
dominates annual
production due to
year-round growth,
especially in warm
Summer/Fall
How does 2005 compare?
Unweighted Marginal Means (some means not observed)
Wilks lambda=.05946, F(119, 590.26)=2.6869, p=.00000
Mean Temperature
Above all
the other
Thermocline
• Mixed layer was
warmer than
GLOBEC Mays
bars denote
0.95years,
confidence
intervalswarmer)
– (2003 wasVertical
later than
all other
therefore
11
Inner
Transitional
Outer
Hinchinbrook
Prince William Sound
10
9
C)
o
8
7
Temperature (
6
5
4
1998
1999
2000
2001
Year
2002
2003
2005
At Gak1 (where we have 10-20 years of data)
mixed layer was warmer than long-term means
MAY
SEPT
Across the line, the average temperature (i.e.
total amount of heat) looks less unusual
13
1
MAY
SEPT
• Nothing unusual about
chlorophyll or zooplankton
• …But higher number of
pteropods (pink salmon food?)
Chlorophyll a (mg m-3)
May 2005
8
7
6
5
4
3
2
1
0
Mean Abundance (No m-3)
1400
1200
1000
Pteropod
Limacina helicina
(May)
PWS
Inner
Trans
Outer
800
600
400
200
0
1998 1999 2000 2001 2002 2003
2005
2001 2002 2003
2004
2005
Neocalanus cristatus
80
60
• Copepods have 6 stages,
more late stages
suggests faster growth
Stage5
20
Stg3
40
Stg4
Percentage Stage
100
0
• 2005 appears to have
faster growth than many
years (for both species)
• Direct measurements
less clear (limited data)
1998 1999 2000 2001 2002 2003 2004 2005
60
0
Stg3
20
Stage4
40
1998 1999 2000 2001 2002 2003 2004 2005
30
Stage Duration (days)
80
Neocalanus plumchrus/flemingeri
Stage5
Percentage Stage
100
25
20
15
10
5
0
2001 2002 2003 2004 2005
6000
4000
2000
1200
1000
PWS
Inner
Trans
Outer
OTHERS
Chaetognatha
Cnidaria
Oikopleura spp.
Calanus pacificus
Eucalanus bungii
Metridia spp.
Paracalanus parva
Pseudocalanus spp.
Oithona similis
0.15
0.10
Paracalanus parva
800
600
400
200
0
1998
0
0.20
Biomass (g m3)
Mean Abundance (No m-3)
Fall 2005
Mean Abundance (No m-3)
Abundance (No m3)
8000
99
00
01
02
03
2005
200
PWS
Inner
Trans
Outer
150
Calanus pacificus
100
50
0
1998
99
00
01
02
03
2005
0.05
Several other “southern
species” also observed
0.00
0
50
100
150
Distance from shore (km)
200
Summary
• The Gulf of Alaska was warmer in 2005 than
typical for a “non-El Niño” year, and this
appears to have favored faster development
of the spring zooplankton
• Much of the North American West coast
experienced such anomalous conditions (with
delayed pelagic production south of Alaska)
• These basin-wide conditions favored the
transport of “southern species” northward into
the Gulf of Alaska
• Implications for Fisheries?