Once upon a time, opposite to today, people were imprecise about what changes had occurred in the Oc

1
Once upon a time, (opposite to today), people
were imprecise about what changes had occurred in
the Ocean but were reasonably sure about what
caused them .
2
It comes up to the shore here from the great
fish pond which is the Icelandic Sea, . and
here in my days there have been two large and
wonderful herring fisheries at different places
in Norway ...although it may well be that in
punishment for the unthankfulness of men it has
moved from place to place, or has been taken away
for a long period. Clergyman Peder Claussøn
Friis (1545-1614)
3
How do Arctic and subarctic processes
interconnect? What underlies present
thinking? by Bob Dickson, CEFAS and Jens
Meincke UHH
SEARCH OSM, Seattle, October 2003
4
Domain of talk Topography kindly provided by
Michael Karcher, A-W-I Bremerhaven
5
Point 1 The climatic forcing of Arctic and
subarctic seas in recent decades has been extreme.
6
Variations in Global Temperature and their
uncertainties,1861- April 2001(land air and sea
surface temperature)
The context during the past century, the global
mean temperature has increased in two main
episodes of warming
7
When we plot air temperature as a function of
latitude and time, two things become clear 1)
the World is warmer. Including 2002, all ten of
the warmest years since records began in 1861
have occurred since 1990 Jones and Moberg, 2003.
2) in the last two decades the distribution of
warming has become global.
Courtesy Tom Delworth, GFDL
8
.and our instrumental and proxy records suggest
that the NAO in the 1990s may have been at a 600
year extreme positive state.
Phil Jones CRU, in press
9
Point 2 Change can be imposed on the Arctic
Ocean from the Nordic seas.
10
Since the change from NAO-negative (1960s) to
NAO-positive (1990s) is associated with a
strengthened southerly airflow west of Norway
Change in winter slp, (NAO) minus (NAO-) from
Dickson et al 2000.
11
.it is unsurprising that the amplifying NAO was
accompanied by a warming of the 2 main Atlantic
water inflows to the Arctic Ocean --- in this
case the upper 500m of the West Spitzbergen
Current west of Svalbard.
Dickson et al 2000
12
T C
and the same irregular warming has affected the
inflow branch flowing through the western Barents
Sea. Harald Loeng IMR Bergen, pers comm
13
Morison et al, 1998 2000
By comparing the 1993 SCICEX data with the new
Gore-Chernomyrdin climatology, Morison et al
showed that the warming had affected the
Atlantic-derived sublayer where the inflow
subducts to spread through the Eurasian basin.
This is the picture that started SEARCH!
and
14
and Karcher et al have pieced together the
spread of warming around the boundary of the
Arctic Ocean in 1980, 1984, 1987 1991,
from Karcher et al 2003.
1984
1980
1987
1991
15
and its continued spread in 1993, 1995, 1996
1999, from Karcher et al 2003.
1993
1995
1996
1999
16
Point 3 localized processes on the Arctic
Shelves can drive extensive changes in the
watermasses of the Arctic Ocean and N. Greenland
Sea
17
Bottom salinity Novaya Semlya
Bottom salinity Storfjord
Advection Atl.Waters
M2-Tide
In the UHH HAMSOM model, bottom-layer (50-100 m)
salinities in the Sankt Anna Trough are found to
respond most to an imposed increase in the inflow
of Atlantic water through the Barents Sea
entrance, while those in the closed basin of the
Storfjord respond most to the imposition of M2
tidal mixing.
Analyses by C.Schrum and K Hatten, UHH
18
Point 4 we have experienced two episodes of
Arctic warming in recent decades, apparently with
quite different causes
19
The historic Russian temperature series from the
Kola Section, spanning more than a Century, show
a first period of protracted warmth in the middle
decades of last century plus a second
less-regular warming over the past 3 decades.
Data from PINRO
(Loeng Ingvaldsen 2002)
20
Bengtsson, Semenov and Johannessen (2003) review
the possible causes of the earlier warming 1.
Not anthropogenic ghg forcing was then only 20
of present and temperatures cooled subsequently
between 1940 and 1960 when ghg forcing was the
same or greater. ? . 2. Dont know if its solar
forcing Observational data only exist for the
last two decades. ? 3. Not volcanicity. Katmai
(1912) would have had a smaller effect on climate
than Pinatubo (1991), and the cooling effect of
Pinatubo disappeared after lt 3 years. ? 4.
Internal variability in the climate system?
Probably. They propose a mechanism involving
increased pressure gradient between Svalbard and
Norway, increased warm water transport to the
Barents Sea and decreased sea-ice cover. ?
21
Aadlandsvik, 2003 pers comm
While its true that there has been a long term
increase in both SW wind component (BSI) and Kola
temperatures since the turn of the century, .
22
the relationship has problems in detail.
Comparing Aadlandsviks Barents Sea Inflow Index
(BSI) with Kola temperatures, we find that they
correlate closely after 1960 but not before.
23
Bjorn Aadlandsvik, IMR Bergen pers comm
30-year moving series show that the relationship
between BSI Index and Kola temperature moves from
negative and not significant in the 1930s-40s
.To positive and significant correlation in the
1970s-80s
24
After 1960, the warming on the Kola Section may
in part be locally driven, since NAO-positive
conditions support strengthened SWerlies across
the entrance to the Barents Sea .
Change in winter slp, (NAO) minus (NAO-) from
Dickson et al 2000.
25
and part remote forcing. Orvik Skagseth
(GRL accepted July 2003) show a close link (r
0.88) between the Nward flow of warm salty water
at Svinoy (62N) and the N Atlantic windstress
curl at 55N, 15 months earlier.
26
So what caused the earlier warming? One
important clue may lie in its geographic
distribution.
27
Long hydrographic records from a) W. Greenland,
b) N. Iceland, c) Faroe-Shetland Channel, d)
Faroes and e) Barents Sea show that a warm salty
wave passed through the Atlantic Northern Gyre
in the middle Decades of the 20th C.
28
And the GISST dataset confirms that the earlier
warmth was largely a feature of the Northern
Gyre. Source Claire Cooper, Hadley Centre
29
The closest fit is with a climatic index from the
Atlantic mid-latitudes, the U Index of Kushnir
Schematic of Kushnirs (1993) U-index
30
Point 5 Arctic change can be imposed on the
Nordic Seas and on the deep/abyssal Atlantic.
31
Current-meter thermistor data from 2000m depth in
the core of the Denmark Strait Overflow show a
dramatic decadal variation in mean temperatures.
These values are not smoothed. Each 30-day mean
is simply the average of 720 hourly values.
32
We believe these temperature changes originate in
the upper waters of the eastern Fram Strait, 2500
km upstream and 3 years earlier
33
and the temperature and salinity of the overflow
core at 2000m off Angmagssalik clearly determine
the density of the DSOW-derived layer of the
abyssal Labrador Sea a further one year later.
34
.so despite the many possible contributory source
s of DSOW shown in Rudels scheme, Recirculating
Atlantic Water (RAW) from the Fram Strait seems
to have been the dominant control on DSOW
variability in recent years. Map from Rudels et
al , 2003
35
Point 6 The freshwater flux from the Arctic to
the North Atlantic doesnt always get through
(i.e we cant just measure efflux through Fram
Strait)
36
the GSA circuit in 1968-82 ...
37
The measured volume flux of ice through Fram
Strait showed a massive peak in 1994-5. Svein
Osterhus, University of Bergen
38
but the path of this record outflow in 1994-95
seems to have differed dramatically from that of
the GSA.
39
1994
1995
Beautifully illustrated in the distributionoff
SSS anomaly in the A-W-I NAOSIM model for
Decembers of 1994-97. Karcher and Gerdes, pers
comm 2003.
1996
1997
40
Meinckes working hypothesis invokes the
contrasting conditions of the East Greenland
Current and Greenland Sea in the 1960s and 1990s
41
Point 7 however, we do believe there has been a
major increase in the outflux of fresh water from
Arctic/subarctic seas over the past 4 decades,
affecting the surface, intermediate, deep and
abyssal layers of the N Atlantic.
42
Schematic of the northern loop of the oceans
Great Conveyor. McCartney et al 1996
The elements of an ASOF freshwater flux array is
funded and is partly in place. Few results
yet.....but we do have one proxy measure of fw
flux from the AR7W Line
43
The offshore density gradient in the 0-150m layer
from Labrador Shelf to the Central Lab Sea is our
only (proxy) measure of the changing fw flux to
the NW Atlantic. This gradient has progressively
steepened with the NAO over the past 4 decades
(equivalent to a 20 incr. In Sgoing transport)
largely thro freshening of shelf upper-Slope
waters. Yashayaevs analysis of AR7W
Density gradient
Density
44
freshening has also affected the system of cold,
dense overflows which spill south from Nordic
Seas to ventilate the deep North Atlantic..
45
Over the past 4 decades, for a variety of reasons
associated with the amplifying NAO the fresh
water accession to the Nordic Seas has increased
steadily
46
Salinity at OWS M, Norwegian Sea, 1950-97,
Courtesy Svein Østerhus, UiB
The result has been a broadscale freshening of
the Nordic Seas which over the past 4 decades has
reached to depths of gt1 km, so is accessible to
the two main overflows which cross the
Greenland-Scotland Ridge.
47
Tapping-off the freshening upper layer of the
Nordic Seas, the two dense overflows that renew
and ventilate the deep ocean have also freshened
over the past 4 decades. Dickson et al, Nature
2002.
48
so that if we construct salinity time series at
intervals along the spreading pathways of both
overflows from their sills to the deep Labrador
Sea
49
we find that the entire system of overflow and
entrainment that ventilates the deep Atlantic has
undergone a remarkably rapid and remarkably
steady freshening over the past four decades.
-15 fresher by 0.015/decade, 1965-2000 A
change in the ocean-climate of sub-arctic seas
has thus been transferred to the deep and
abyssal ocean at the headwaters of the Great
Conveyor Dickson et al 2002
50
NAO-
NAO
The resulting full-depth change in the Labrador
Sea salinity is believed to be the largest change
in the oceanographic record. By 1992, equal to
adding an extra 6 m of fresh water at the sea
surface Lazier 1995.
51
The result has been a dramatic shift in the ? -S
relation for waters of the NW Atlantic. Igor
Yashayaev, unpublished
52
Point 8 There are some signs of effects on the
Atlantic circulation.
53
Point 8 There are some signs of effects on the
Atlantic circulation a) possible slowdown of
the eastern overflow.
54
This hypothesis is based on proxy evidence, and
applies only to the eastern overflow. There, the
depth of the ?t28.0 isopycnal in the upstream
reservoir of the Norwegian Sea controls the
pressure head that drives overflow through the
Faroe-Bank Channel (Hansen et al 2001).
55
Depth of the ?t28.0 isopycnal at OWS M
At OWS M, the ?t 28.0 isopycnal has steadily
deepened with time, by ?70m in 50 years, (Hansen
et al 2001).
56
Hansen et al (2001) use this finding to suggest
that the coldest, deepest part of the eastern
overflow may have decreased by 20 since 1950.
57
Point 8 There are some signs of effects on the
Atlantic circulation a) the eastern
overflow ..but not yet the western.
58
There is no such evidence from the western
overflow through Denmark Strait. There, the 187
monthly means of flow speed collected from the
overflow core since 1986 (z ?2000m) show little
sign of seasonal variability..
59
Neither has there been any obvious change in the
transport of the overflow core.
60
Point 8 There are some signs of effects on the
Atlantic circulation c) changes in the deep
density field
61
1966-67
1994
Effects on watercolumn density (so, potentially,
on circulation) have been observed. e.g.the
deepest densities in the Labrador Sea in the
Newfoundland Basin (above) have decreased between
the 1960s and 1990s.... Igor Yashayaev, pers
comm
62
as they have on the Woods-Hole Bermuda line
through the West Atlantic .
Curry, Dickson Yashayaev, in press.
63
Point 8 Regarding effects on the Meridional
Overturning Circulation (MOC) we remain
myopic/agnostic...
64
unless you are Discover Magazine which seems
sure!
65
The thing we have our eye on ----maybe
wrongly----is the idea that a change in the MOC
will be associated with some measurable change in
the trans-ocean density gradient. HadCM3 finds a
very close correlation between Atlantic
overturning rate and the S-N gradient of steric
height from 30S - 60N through the W Atlantic.
(Thorpe et al 2001)
66
Choosing a suitable Thorpe et al transect
through the western ocean ...
67
THC Overturning vs Atlantic Meridonal Steric
Gradient in HADCM 3(Thorpe et al 2001)
1970
1995
20 cm
40 cm
and mapping the observed steric gradient changes
onto the Thorpe et al results, we find little
change in Atlantic MOC strength over the past 30
years may have even strengthened a little.

68
Point 9 The freshening of European Arctic and
subarctic seas may not be merely an Atlantic
event but the strong local expression of a change
in the Global Water Cycle.
69

• A warmer atmosphere will carry more water vapor,
  because of the exponential increase of vapor
  pressure with temperature.
• Thus it is expected that the Global Water Cycle
  Will Accelerate With Global Warming
• An enhanced water cycle will change the
  distribution of salinity in the upper ocean.

Ray Schmitt,WHOI pers comm
70
(as far as weve got!) So is this it? Salinity
change since the 1960s along the same Thorpe
line from Labrador Sea to the Weddell Sea shows
freshening towards both poleward margins, and
increasing salinities at low latitudes ----the
sort of change we might expect from an
accelerating water cycle. (work in
progress) Curry, Dickson and Yashayaev, in press
71
Point 10 These changes on the scale of oceans
and decades have been accompanied by massive
changes in the great fisheries of Arctic
subarctic seas.
72
The West Greenland cod fishery is highly
intermittent, relying on the periodic transfer of
warmth and larvae from SW Iceland during periods
when the Irminger Current is strong. Icelandic
larvae may return as adults.
73
Between cod fishery periods at W Greenland, the
fish are almost totally absent from the W
Greenland Banks.

• In 1850 the cod were practically non-existant
  (Jensen and Hansen, 1931)
• Between 1866-1881, 31 fishing voyages from
  Gloucester Massachusetts to the Davis Strait
  found insufficient to warrant their being
  salted (Scudder, 1883).
• In 1901, V. Thorson of the Greenland
  Administration found no cod on Fylla Bank.
• In 1906 two Faroes cutters under Napoleon
  Andreasen of Thorshaven found not a single cod on
  the Banks from Holsteinborg to Godthab I have
  never at any place searched longer or more keenly
  after fish than here at the coast of Greenland to
  be rewarded with such a poor result.
• In 1908 and 1909 Ad. S Jensen and the brig Tjalfe
  found not a single fish on the Banks or along
  their seaward margins
• In 1913, V Thorson fished the Banks in vain on
  the steamer Hans Egede

74

• Then back they came
• in 1922-24, the Danish inspection vessels Fylla
  and Islands Falke find quantities of cod on Fylla
  bank
• in 1925 and 1925 cod shoals were also found by
  Johann Hjort aboard Michael Sars and Dana
• in 1925 the cod were found spawning for the first
  time from Fiskenaes Bank to Store Hellefiske Bank
  (Jensen 1926)
• By 1928-29 the fish had spread right up to
  Holsteinborg and Disko Bay
• By the late 1950s, the international catch
  exceeded 400,000 tonnes per year.

75
Spread of Cod at West Greenland

• 1900 Cape Farewell Fiskenes Bank
• 1917-18 Frederikshaab
• 1919 Godhaab
• 1922 Sukkertoppen
• 1927-30 Christianshaab and first direct evidence
  of spawning DANA 1925
• 1931-36 Umanak
• Late 1930s Upernavik
• Late 1960 decline and retreat

76
The local and international catch of cod at West
Greenland rose with the temperature on the Banks
77
Large Cod taken in the Godthåbsfjord W Greenland
in 1951. Kindly provided by Dr. Kai Wieland,
Greenland Institute of Natural Resources Nuuk,
Greeenland
78
Though other great fisheries of subarctic seas
underwent apparently-similar changes, they proved
to be largely due to Man (overfishing).
79
But Fiksen and Slotte (2002) show that
temperature explains only 6-9 of the variation.
They suggest that the collapse of the SSB from 16
Mt in 1945 to 2000 t in 2000 was due to heavy
fishing pressure on the adults.
Brander points out however (2003) that the
decline of the SSB preceded the peak in adult
fishing mortality.
.and that the start of the decline coincided
with heavy fishing pressure on juveniles. (data
from Toresen and Ostvedt, 2000)
The variation in the spawning stock biomass (SSB)
of the Norwegian spring spawned herring stock
appears to co-vary with temperature over the past
Century (Toreson and Ostvedt, 2000).
80
(No Transcript)