Arctic Climate Seminar Series
September 2005 - June 2007
The major goals of this seminar series are to provide WHOI scientists and students with the basic knowledge about the most important problems of climate variability in the Arctic, and to enhance their ability and increase their participation in finding the solutions to these problems. WHOI scientists can successfully contribute to Arctic science in two ways: via development and implementation of new instruments allowing year-round observations of arctic processes under sea ice; and through theoretical and numerical studies that will formulate and help solve fundamental questions of arctic climate variability.
For more information please visit the WHOI Arctic Group website at: http://www.whoi.edu/science/PO/arcticgroup/
The Arctic Climate Seminar Series - Schedule
June 5, 2007
Peter Jones
Ocean Sciences Division
Bedford Institute of Oceanography
Freshwater outflow from the Arctic: Implications for the Global Conveyor Belt
Clark 507, Quissett Campus, 3:00 p.m.
Abstract:
The Atlantic Ocean experiences more evaporation than
precipitation. Much of the excess evaporated water, which falls as rain
into the Pacific and Arctic oceans and into river drainage basins that feed into the Arctic Ocean, is returned to the North Atlantic through the Arctic Ocean and subsequently into the Nordic
and Labrador seas. It has been suggested
that changes in the amount of fresh water flowing from the Arctic Ocean could alter deep-water formation in
these headwaters of global thermohaline circulation. The fresh water
sources include Pacific water, river water and sea ice meltwater. How
they are distributed within the Arctic Ocean, how they vary, and how they are
partitioned into the various pathways are fundamental for obtaining a better
understanding of how they may affect deep convection in the Nordic and Labrador seas. Using tracers we
determine pathways, inventories, and, to a limited extent, the variability of
fresh water within the Arctic Ocean and exiting from it. One conclusion is that climate change
scenarios should not use a single parameter (salinity) for representing fresh
water leaving the Arctic Ocean since the different fresh
water sources are subject to different forcing and thus would potentially
respond to climate change in different ways.
May 15, 2007
Peter Schlosser
Columbia University, Lamont-Doherty Earth Observatory
'Recent Changes In The Arctic Hydrosphere: Implications For The Global Ocean Circulation'
Clark 507, Quissett Campus, 3:00 p.m.
The changes in the Arctic Ocean are not isolated features of a remote ocean basin. Significant changes in water mass properties have been observed in the Nordic seas and the North Atlantic. They raise the question of a possible slowdown of the Meridional Overturning Circulation in the Atlantic Ocean (the headwaters of the ‘Great Ocean Conveyor Belt’). Such changes are not unexpected and have been predicted by numerical models. In fact, simulations of the future MOC using coupled models with greenhouse gas forcing project even stronger changes in the decades and centuries ahead.
This presentation will review the observed changes in the Arctic hydrosphere with emphasis on their link to lower latitudes. A key question for the future will be if a slowdown of the MOC in a warmer world would lead to a cooling of the surface ocean and the atmosphere in the northern hemisphere.
March 15, 2007
Koji Shimada
Japan Marine Science and Technology Center (JAMSTEC)
"Catastrophic
reduction of sea-ice cover in the Pacific sector of the Arctic Ocean"
Clark 507,
10:00 a.m.
Abstract:
February 1, 2007
James Morison
Polar Science
Center ,
Applied Physics Laboratory,
University of Washington , Seattle
"Bottom Pressure Measurements and Indications of Change in the Arctic Ocean"
Clark 507, 10:00 a.m.
Abstract:
In the late 1980s and through the 1990s we saw major shifts in the Arctic Ocean . The influence of Atlantic Water in the Arctic Ocean became more widespread and intense and the pattern of water circulation and ice drift shifted, resulting in a more cyclonic circulation. These changes became manifest in the central Arctic near the North Pole as increases in upper ocean salinity and Atlantic Water temperature. They occurred in concert with a decrease in surface atmospheric pressure. With the aim of helping to track such changes, we have undertaken in situ ocean bottom pressure measurements and the analysis of Gravity Recovery and Climate Experiment (GRACE) data. For the in situ measurements we have developed, with the help of the NOAA tsunami early warning system group, an Arctic Bottom Pressure Recorder (ABPR), which is suitable for deployment through pack ice. The ABPRs are equipped with acoustic modems to allow annual data recovery while leaving the instruments undisturbed on the bottom for up to 3 years. Recovery of the first year of data from gauges installed near the North Pole was achieved in April 2006. The comparison between GRACE- derived bottom pressure at the North Pole and the ABPR data is quite good. The GRACE data are filtered with a 400 km radius Gaussian filter, so their footprint easily covers both ABPR locations. At this scale, the two ABPR records are highly correlated. Both GRACE and the ABPRs show a declining bottom pressure trend in 2005-2006. The complete GRACE record indicates this has been going on since the start of the GRACE record and amounts to about a 10 cm decrease in bottom pressure from 2002 to 2006. We believe this trend is largely associated with a steric change due to a drop in upper ocean salinity near in the central Arctic Ocean . The change in hydrography near the Pole has been tracked for the last 6 years by the North Pole Environmental Observatory (NPEO). The NPEO record shows a reduction in upper ocean salinity to near the pre-1990s climatology. This is arguably related to ocean circulation changes associated with the decline in the Arctic Oscillation (AO) index. We have averaged all the NPEO hydrographic casts taken each year since 2000 within 400 km of the Pole, and computed the average bottom pressure change associated with the average density changes in each year. The agreement with the GRACE and ABPR trends is good through 2005. This suggests sea level changes are not contributing greatly to the bottom pressure change at the Pole, a conclusion reinforced by preliminary analysis of sea surface height trends estimated from ICESat data. We have also investigated the effect on bottom pressure of a hypothetical return to pre-1990s hydrography over a larger area of the Arctic Ocean . We find reasonable agreement with the spatial distribution of bottom pressure trends from GRACE, especially a decrease in bottom pressure in the Makarov Basin associated presumably with the return of less saline, Pacific-derived upper ocean water to that region. Associated hypothetical trends in sea surface height (SSH) are generally smaller and in an opposite sense from the bottom pressure trends, and their spatial pattern is roughly consistent with an observed shift to a more anticyclonic ice drift.October 26, 2006
Greg Holloway
Institute of Ocean Sciences, Canada
“Arctic Ocean Models Intercomparison Project.
Getting somewhere?”
Clark 507, 3:00 p.m.
Abstract:
This cooperation among Arctic modelers at 16 institutions
in 9 countries seeks to identify differences among models' outputs
and differences from Arctic ocean/ice observations. The goal is
to recognize systematic deficiencies as a step toward better models.
Great eh? Turns out to be really really hard to do.
We catalog the stunning range of models' differences even when efforts have been made to set up and run each model in similar ways. Already this is sobering in terms of models' individual believability. Unfortunately most differences go in every which direction for what reasons no one knows. Ugh.
Recently some clearer results emerge. First, all models are seen to fail systematically with respect to sustaining cold haloclines. Although there are many, varied mixed layer and shelf-basin exchange assumptions, realistic haloclines elude us all, implying an important (but unknown!) missing physics. Second, AOMIP outputs segregate into two disjoint sets based upon what is assumed for subgridscale friction. Models employing traditional frictional closures exhibit ambivalent, readily reversible circulation patterns, while models with statistical mechanical closure exhibit strong, persistent cyclonic rim currents".Third, Arctic tides are shown to contribute to enhanced ventilation of Atlantic Layer heat, in part melting ice. Ice loss is offset by increased growth due to periodic openings and closing of leads.
October 24, 2006
Rüdiger Gerdes
Alfred Wegener Institute for Polar and Marine Research
“100 years of simulated
history of Arctic fresh water reservoirs”
Clark 507, 3:00 p.m.
Hindcast simulations of the Arctic ocean-sea ice system for the last five to six decades indicate large fluctuations in sea ice volume and liquid fresh water storage. Both reservoirs exhibit maximum content in the 1960s and a long-term downward trend that continues today. Both temperature and wind forcing were responsible for the sea ice volume maximum in the 1960s. The long term trend is mostly due to increasing surface air temperatures. On the other hand, the liquid fresh water maximum followed a near-breakdown of exchanges through Fram Strait. The further development can be described as a slow adjustment back towards normal conditions. The simulation results depend sensitively on the treatment of the surface fresh water fluxes, an Achilles heal of virtually every ocean-sea ice hindcast.
Over the whole simulation period, none of the reservoirs shows a trend with values in the 1950s being similar to those in the 1990s. Longer time series are necessary to better distinguish natural variability and externally forced trends. Reconstructed atmospheric forcing data are used to drive the NAOSIM ocean-sea ice model and the results are validated with historical observations of sea ice extent. A clear downward trend in ice volume exists over the 20th century. This result is consistent with the vast majority of IPCC simulations for the 20th century climate.
July 25, 2006
Dmitry Dukhovskoy
Florida State University
Center for Ocean-Atmospheric Prediction Studies
“A Mechanism of Decadal Variability of the Arctic
Ocean-Greenland Sea Atmosphere-Ice-Ocean System”
Clark 507, 3:00 p.m.
A mechanism of decadal variability in the Artic Ocean - Greenland Sea ice-ocean-atmosphere system is discussed. The motivating hypothesis is that the behavior of the system is auto-oscillatory with a quasi-decadal periodicity. This system oscillates between two circulation regimes: the Anticyclonic Circulation Regime (ACCR) and the Cyclonic Circulation Regime (CCR). During the ACCR interaction between the basins is weak: heat flux to the Arctic Ocean and freshwater flux to the Greenland Sea are relatively low. Weak interaction leads to growth of surface air temperature and dynamic height gradients between these regions. Strong gradients promote interaction such that intense heat flux to the Arctic from the Greenland Sea results in the shift to the CCR. After several years of intense interaction, between-basin gradients have eroded, and the interaction fades. The CCR transits to the ACCR. The conceptual mechanism of Arctic decadal variability has been reproduced in a simple model of the Arctic Ocean and Greenland Sea, coupled to a thermodynamic sea ice model and an atmospheric model. Solutions obtained from numerical simulations with seasonally varying forcing, for scenarios with high and low interaction between the regions, reproduced the major anomalies in the ocean thermohaline structure, sea ice volume, and fresh water fluxes attributed to the ACCR and CCR.
July 13, 2006
Richard Moritz
Polar Science Center
Applied Physics Lab
University of Washington
“Variability of sea-ice draft at the North Pole
Environmental Observatory, 2001-2005”
Clark 201, Fuglister, 3:00 p.m.
Abstract:
The draft of sea-ice was measured with an Upward Looking
Sonar (ULS) attached to a fixed mooring near the North Pole during
April, 2001-April, 2005. The time series data are aggregated
and processed statistically to produce estimates of the mean ice
thickness, modes, variance and thickness distribution at two-week
intervals. The sample statistics reveal significant annual
cycles, interannual variability and changes on shorter time scales.
The mean values are in the range of estimates published by Rothrock,
et al. 1999 based on submarine-mounted ULS profile data acquired
in the 1990's. The interannual and shorter-term changes are correlated
with the advection of ice age, estimated independently from measurements
by the International Arctic Buoy Program and the SSM/I passive microwave
sensor. Temporal variations in the monthly means are compared with
estimates from a coupled ice/ocean model forced by atmospheric reanalysis
data.
May 11, 2006
Mark C. Serreze
University of Colorado
Boulder, Colorado
Clark 507, 11:00 a.m.
Abstract:
The Arctic is a complex system, characterized by myriad interactions and feedbacks between its atmosphere, lands, ocean, and cryosphere. Nevertheless, we can learn much about how the Arctic works by paring the system down to bare essentials. Atmospheric transports work in the opposite sense. Poleward-moving air cools, condenses, and precipitates over the Arctic Ocean and the vast surrounding land area that drains into it. From autumn through winter, most precipitation is stored as snow. As the atmosphere and surface warm in spring, there is an immense river discharge to the Arctic Ocean. This helps to keep the ocean surface fresh, which makes it easy for sea ice to form in autumn and winter, which in turn impacts on the Arctic large-scale heat budget.
February 9, 2006
Dr. Ignatius Rigor
Polar Science Center
Applied Physics Laboratory
University of Washington
"Interdecadal Variations in Arctic Sea Ice"
Clark 507, 10:00 a.m.
Abstract:
The extent of arctic sea ice during summer has declined to record minima during the past decade. Five of the lowest minima in the last 100 years were observed during this period, and a new record minimum was set in September 2005. These changes have a profound impact on many other aspects of Arctic and global climate, ecology, and society. For example, many plant and animal species have been migrating further north, and the lack of sea ice during summer makes the Arctic Ocean, or more pertinently, the Chukchi and Beaufort seas north of Alaska , more accessible for navigation. Can we predict these minima?
These minima may be attributed
to global warming (e.g. the Arctic Climate Impacts Assessment Report
2004), but this decline may also be attributed to a change in the
wind driven circulation of Arctic sea ice. In a series of papers,
we showed that the prior winter Arctic Oscillation (AO) conditions
explained most of the trends in summer sea ice extent in the Eurasian
sector of the Arctic Ocean (Rigor et al. 2002), while in the Alaskan
sector the recent extreme minima may be due to the drift of younger,
thinner ice towards the Alaskan coast during the recent predominance
of high to moderate AO conditions (Rigor and Wallace, 2004).
In this presentation, we plan to show
some of the observed changes in Arctic climate, and relate these
changes to the North Atlantic / Arctic Oscillation. We will also
show how these relationships (correlations) may help us explain
our long-term (1900-present) SAT and sea ice extent records. And
finally we will show how these relationships may be used to improve
our operational capability to predict Arctic sea ice conditions
on weekly to seasonal time scales.
December 15, 2005
Dr. Don Perovich
Cold Regions Research and Engineering Laboratory
Hanover, New Hampshire
"The Heat and Mass Balance of Arctic Sea Ice"
Clark 507, 10:00 a.m.
Abstract:
Sea ice covers much of the Arctic Ocean . This extensive, but thin, floating ice cover profoundly affects energy exchange between the atmosphere and the ocean. Large-scale climate models indicate that the Arctic sea ice cover may be both a harbinger and an amplifier of climate change. Recent studies indicate that the Arctic sea ice cover is undergoing significant reductions in both ice extent and thickness. These changes may have impacts beyond the Arctic through positive feedback mechanisms such as the ice-albedo feedback. We will discuss the ongoing changes in the Arctic sea ice cover from the perspective of the heat and mass balance of the ice.September 27, 2005
Dr. W.R. Peltier
Department of Physics
University of Toronto
"Rapid Climate Change and the Arctic: Perspectives
from Paleoclimatology"
Clark 507, Quissett Campus, WHOI at 3:00 p.m.
Abstract:
It now appears that the "trigger" for the onset of the Younger-Dryas cold reversal that interrupted the transition from full glacial to the modern (Holocene) climate regime, was caused by the arrival of an intense pulse of freshwater, of strength approaching 0.3 Sv, into the Arctic Ocean through the McKenzie River outlet. I will discuss the analyses that have been performed that support this conclusion and demonstrate, using a fully coupled atmosphere-ocean climate model, that the Atlantic MOC would have been sharply reduced in strength as a consequence. The expected response in terms of surface atmospheric temperature nicely reconciles the available proxy data which require the response of the climate system to have been at least hemispheric in spatial scale. These paleoclimatological aspects of the presentation will be augmented by a discussion of the main mode(s) of Arctic climate variability under both modern and glacial conditions.