The formation and maintenance of the North Water Polynya

Abstract

This paper investigates the formation and maintenance of the North Water Polynya, Baffin Bay in winter using a multi‐category sea‐ice model coupled with the Princeton ocean model. Monthly climatological atmospheric data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis provides the forcing. An objectively‐analysed climatology provides the initial ocean temperature and salinity. Wind stress drives the ice in a cyclonic gyre around northern Baffin Bay. Localized regions of thin ice form where wind drives ice away from coastlines or fast ice. The regions of thin ice are characterized by enhanced ice growth, exceeding 1.2 m mo^?1. In the regions of thin ice, surface ocean heat flux is also enhanced and is between 30–60 W m^?2. Surface heat flux is, in part, attributable to convective mixing and entrainment driven by ice growth. The surface heat flux reflects advection of the warm West Greenland Current. Heat and salt balances show that horizontal advective exchange counterbalances surface fluxes of heat and salt.     

Potential role of Atlantic Warm Pool-induced freshwater forcing in the Atlantic Meridional Overturning Circulation: ocean–sea ice model simulations

Recent studies have indicated that the multidecadal variations of the Atlantic Warm Pool (AWP) can induce a significant freshwater change in the tropical North Atlantic Ocean. In this paper, the potential effect of the AWP-induced freshwater flux on the Atlantic Meridional Overturning Circulation (AMOC) is studied by performing a series of ocean–sea ice model experiments. Our model experiments demonstrate that ocean response to the anomalous AWP-induced freshwater flux is primarily dominated by the basin-scale gyre circulation adjustments with a time scale of about two decades. The positive (negative) freshwater anomaly leads to an anticyclonic (cyclonic) circulation overlapping the subtropical gyre. This strengthens (weakens) the Gulf Stream and the recirculation in the interior ocean, thus increases warm (cold) water advection to the north and decreases cold (warm) water advection to the south, producing an upper ocean temperature dipole in the midlatitude. As the freshwater (salty water) is advected to the North Atlantic deep convection region, the AMOC and its associated northward heat transport gradually decreases (increases), which in turn lead to an inter-hemispheric SST seesaw. In the equilibrium state, a comma-shaped SST anomaly pattern develops in the extratropical region, with the largest amplitude over the subpolar region and an extension along the east side of the basin and into the subtropical North Atlantic. Based on our model experiments, we argue that the multidecadal AWP-induced freshwater flux can affect the AMOC, which plays a negative feedback role that acts to recover the AMOC after it is weakened or strengthened. The sensitivity of AMOC response to the AWP-induced freshwater forcing amplitude is also examined and discussed.     

Influences of Freshwater from Major Rivers on Global Ocean Circulation and Temperatures in the MIT Ocean General Circulation Model

Responses of global ocean circulation and temperature to freshwater runoff from major rivers were studied by blocking regional runoff in the global ocean general circulation model(OGCM)developed at the Massachusetts Institute of Technology.Runoff into the tropical Atlantic,the western North Pacific,and the Bay of Bengal and northern Arabian Sea were selectively blocked.The blocking of river runoff first resulted in a salinity increase near the river mouths(2 practical salinity units).The saltier and,therefore,denser water was then transported to higher latitudes in the North Atlantic,North Pacific,and southern Indian Ocean by the mean currents.The subsequent density contrasts between northern and southern hemispheric oceans resulted in changes in major ocean currents.These anomalous ocean currents lead to significant temperature changes(1°C-2°C)by the resulting anomalous heat transports.The current and temperature anomalies created by the blocked river runoff propagated from one ocean basin to others via coastal and equatorial Kelvin waves.This study suggests that river runoff may be playing an important role in oceanic salinity,temperature,and circulations;and that partially or fully blocking major rivers to divert freshwater for societal purposes might significantly change ocean salinity,circulations,temperature,and atmospheric climate.Further studies are necessary to assess the role of river runoff in the coupled atmosphere-ocean system.     

Interdecadal climate variability in the subpolar North Atlantic

The statistical relationships between various components of the subpolar North Atlantic air-sea-ice climate system are reexamined in order to investigate potential processes involved in interdecadal climate variability. It is found that sea surface temperature anomalies concentrated in the Labrador Sea region have a strong impact upon atmospheric sea level pressure anomalies over Greenland, which in turn influence the transport of freshwater and ice anomalies out of the Arctic Ocean, via Fram Strait. These freshwater and ice anomalies are advected around the subpolar gyre into the Labrador Sea affecting convection and the formation of Labrador Sea Water. This has an impact upon the transport of North Atlantic Current water into the subpolar gyre and thus, also upon sea surface temperatures in the region. An interdecadal negative feedback loop is therefore proposed as an internal source of climate variability within the subpolar North Atlantic. Through the lags associated with the correlations between different climatic components, observed horizontal advection time scales, and the use of Boolean delay equation models, the time scale for one cycle of this feedback loop is determined to have a period of about 21 years.     

Projection of subtropical gyre circulation and associated sea level changes in the Pacific based on CMIP3 climate models

For all of the IPCC Special Report on Emission Scenarios (SRESs), sea level is projected to rise globally. However, sea level changes are not expected to be geographically uniform, with many regions departing significantly from the global average. Some of regional distributions of sea level changes can be explained by projected changes of ocean density and dynamics. In this study, with 11 available Coupled Model Intercomparison Project Phase 3 climate models under the SRES A1B, we identify an asymmetric feature (not recognised in previous studies) of projected subtropical gyre circulation changes and associated sea level changes between the North and South Pacific, through analysing projected changes of ocean dynamic height (with reference to 2,000 db), depth integrated steric height, Sverdrup stream function, surface wind stress and its curl. Poleward expansion of the subtropical gyres is projected in the upper ocean for both North and South Pacific. Contrastingly, the subtropical gyre circulation is projected to spin down by about 20 % in the subsurface North Pacific from the main thermocline around 400 m to at least 2,000 m, while the South Pacific subtropical gyre is projected to strengthen by about 25 % and expand poleward in the subsurface to at least 2,000 m. This asymmetrical distribution of the projected subtropical gyre circulation changes is directly related to differences in projected changes of temperature and salinity between the North and South Pacific, forced by surface heat and freshwater fluxes, and surface wind stress changes.     

NAO–ocean circulation interactions in a coupled general circulation model

The interplay between the North Atlantic Oscillation (NAO) and the large scale ocean circulation is inspected in a twentieth century simulation conducted with a state-of-the-art coupled general circulation model. Significant lead–lag covariance between oceanic and tropospheric variables suggests that the system supports a damped oscillatory mode involving an active ocean–atmosphere coupling, with a typical NAO-like space structure and a 5 years timescale, qualitatively consistent with a mid-latitude delayed oscillator paradigm. The two essential processes governing the oscillation are (1) a negative feedback between ocean gyre circulation and the high latitude SST meridional gradient and (2) a positive feedback between SST and the NAO. The atmospheric NAO pattern appears to have a weaker projection on the ocean meridional overturning, compared to the gyre circulation, which leads to a secondary role for the thermohaline circulation in driving the meridional heat transport, and thus the oscillatory mode.     

The stability of the North Atlantic thermohaline circulation in a coupled ocean-atmosphere general circulation model

 The stability of the Atlantic thermohaline circulation against meltwater input is investigated in a coupled ocean-atmosphere general circulation model. The meltwater input to the Labrador Sea is increased linearly for 250 years to a maximum input of 0.625 Sv and then reduced again to 0 (both instantaneously and linearly decreasing over 250 years). The resulting freshening forces a shutdown of the formation of North Atlantic deepwater and a subsequent reversal of the thermohaline circulation of the Atlantic, filling the deep Atlantic with Antarctic bottom water. The change in the overturning pattern causes a drastic reduction of the Atlantic northward heat transport, resulting in a strong cooling with maximum amplitude over the northern North Atlantic and a southward shift of the sea-ice margin in the Atlantic. Due to the increased meridional temperature gradient, the intertropical convergence zone over the Atlantic is displaced southward and the westerlies in the Northern Hemisphere gain strength. We identify four main feedbacks affecting the stability of the thermohaline circulation: the change in the overturning circulation of the Atlantic leads to longer residence times of the surface water in high-northern latitudes, which allows them to accumulate more precipitation and runoff from the continents. As a consequence the stratification in the North Atlantic becomes more stable. This effect is further amplified by an enhanced northward atmospheric water vapour transport, which increases the freshwater input into the North Atlantic. The reduced northward oceanic heat transport leads to colder sea-surface temperatures and an intensification of the atmospheric cyclonic circulation over the Norwegian Sea. The associated Ekman transports cause increased upwelling and increased freshwater export with the East Greenland Current. Both the cooling and the wind-driven circulation changes largely compensate for the effects of the first two feedbacks. The wind-stress feedback destabilizes modes without deep water formation in the North Atlantic, but has been neglected in almost all studies so far. After the meltwater input stops, the North Atlantic deepwater formation resumed in all experiments and the meridional overturning returned within 200 years to a conveyor belt pattern. This happened although the formation of North Atlantic deep water was suppressed in one experiment for more than 300 years and the Atlantic overturning had settled into a circulation pattern with Antarctic bottom water as the only source of deep water. It is a clear indication that cooling and wind-stress feedback are more effective, at least in our model, than advection feedback and increased atmospheric water vapour transport. We conclude that the conveyor belt-type thermohaline circulation seems to be much more stable than hitherto assumed from experiments with simpler models. Received 31 January 1996/Accepted 22 August 1996     

Convection induced long term freshening of the subpolar North Atlantic Ocean

This paper is mainly concerned with the understanding and attribution of the recent observed freshening trend in the subpolar North Atlantic Ocean. From previous coupled model studies and an analysis of the long HadCM3 control simulation, it seems unlikely that this freshening trend is a direct consequence of anthropogenically forced climate change. It is shown in this paper that the subpolar North Atlantic can be freshened to the observed degree without invoking substantial large-scale surface freshwater flux changes. The source of freshening can come from a freshwater redistribution within the Arctic/subpolar North Atlantic. The redistribution (involving both liquid water and sea ice) is carried by a perturbed ocean circulation change in the subpolar seas and triggered by deep convection in the Labrador Sea. The freshening can be widespread but mainly in the north and northwest of the subpolar North Atlantic. A sustained 30–40 years freshening trend can be easily identified in specific locations such as the Labrador Sea or in the basin wide integral of freshwater storage. At the peak, the model subpolar North Atlantic can hold around 10,000 km³ of extra freshwater. An analysis of 1,400 years HadCM3 control simulation also reveals a good correlation between freshwater content anomalies and gyre transport in the subpolar North Atlantic on decadal timescales. A general mechanism involving circulation regime changes and freshwater redistribution between the subpolar North Atlantic and the Arctic/Nordic Seas is proposed, which can resolve a number of seemingly contradictory observed changes in the North Atlantic and contributes to the longer term goal of a full understanding of recent North Atlantic fresh water changes.     

A 20-year coupled ocean-sea ice-atmosphere variability mode in the North Atlantic in an AOGCM

In order to understand potential predictability of the ocean and climate at the decadal time scales, it is crucial to improve our understanding of internal variability at this time scale. Here, we describe a 20-year mode of variability found in the North Atlantic in a 1,000-year pre-industrial simulation of the IPSL-CM5A-LR climate model. This mode involves the propagation of near-surface temperature and salinity anomalies along the southern branch of the subpolar gyre, leading to anomalous sea-ice melting in the Nordic Seas, which then forces sea-level pressure anomalies through anomalous surface atmospheric temperatures. The wind stress associated to this atmospheric structure influences the strength of the East Greenland Current across the Denmark Strait, which, in turn, induces near-surface temperature and salinity anomalies of opposite sign at the entrance of the Labrador Sea. This starts the second half of the cycle after approximatively 10 years. The time scale of the cycle is thus essentially set by advection of tracers along the southern branch of the subpolar gyre, and by the time needed for anomalous East Greenland Current to accumulate heat and freshwater anomalies at the entrance of the Labrador Sea. The Atlantic meridional overturning circulation (AMOC) does not play a dominant role in the mode that is confined in the subpolar North Atlantic, but it also has a 20-year preferred timescale. This is due to the influence of the propagating salinity anomalies on the oceanic deep convection. The existence of this preferred timescale has important implications in terms of potential predictability of the North Atlantic climate in the model, although its realism remains questionable and is discussed.     

On the seesaw in interannual variability of upper ocean heat advection between the North Atlantic Subpolar Gyre and the Nordic Seas

In this study we investigate the interannual variability of the heat content of the upper North Atlantic and the main factors, which influence the observed variability: the ocean-atmosphere heat exchange and the ocean heat transport. The data from the combined in situ and satellite dataset ARMOR-3D, and from the ocean reanalyzes ORAS5 and SODA3 (two versions) show a similar decadal interannual variability of the heat content, as well as of oceanic heat transports the study regions, though the mean values may differ. The observed variations are linked to the North Atlantic Oscillation Index (NAOI). The current velocity of the North Atlantic, East Greenland and Labrador currents of the Subpolar Gyre increases with the NAOI, but the velocity of the Irminger and West Greenland currents decreases. This forms a seesaw of heat advection by the North Atlantic Current between the Subpolar Gyre and Nordic Seas. In the Subpolar gyre during the periods of high NAOI, this negative anomaly of the oceanic heat convergence adds to the intensified sea-surface heat release to the atmosphere, together effectively reducing the upper ocean heat content. The upper ocean heat content of the Norwegian Sea shows practically no link to the NAOI, in spite of a somewhat larger oceanic heat flux across its southern boundary linked to high NAOI.     

Decadal fingerprints of freshwater discharge around Greenland in a multi-model ensemble

The recent increase in the rate of the Greenland ice sheet melting has raised with urgency the question of the impact of such a melting on the climate. As former model projections, based on a coarse representation of the melting, show very different sensitivity to this melting, it seems necessary to consider a multi-model ensemble to tackle this question. Here we use five coupled climate models and one ocean-only model to evaluate the impact of 0.1 Sv (1 Sv = 10⁶ m³/s) of freshwater equally distributed around the coast of Greenland during the historical era 1965–2004. The ocean-only model helps to discriminate between oceanic and coupled responses. In this idealized framework, we find similar fingerprints in the fourth decade of hosing among the models, with a general weakening of the Atlantic Meridional Overturning Circulation (AMOC). Initially, the additional freshwater spreads along the main currents of the subpolar gyre. Part of the anomaly crosses the Atlantic eastward and enters into the Canary Current constituting a freshwater leakage tapping the subpolar gyre system. As a consequence, we show that the AMOC weakening is smaller if the leakage is larger. We argue that the magnitude of the freshwater leakage is related to the asymmetry between the subpolar-subtropical gyres in the control simulations, which may ultimately be a primary cause for the diversity of AMOC responses to the hosing in the multi-model ensemble. Another important fingerprint concerns a warming in the Nordic Seas in response to the re-emergence of Atlantic subsurface waters capped by the freshwater in the subpolar gyre. This subsurface heat anomaly reaches the Arctic where it emerges and induces a positive upper ocean salinity anomaly by introducing more Atlantic waters. We found similar climatic impacts in all the coupled ocean–atmosphere models with an atmospheric cooling of the North Atlantic except in the region around the Nordic Seas and a slight warming south of the equator in the Atlantic. This meridional gradient of temperature is associated with a southward shift of the tropical rains. The free surface models also show similar sea-level fingerprints notably with a comma-shape of high sea-level rise following the Canary Current.     

Interannual variability in the 1990s in the northern Atlantic and Nordic Seas

A global fine resolution curvilinear ocean model, forced by NCEP Re-Analysis fluxes, is used to study changes in the circulation of the Nordic Seas and surrounding ocean basins during 1994-2001. The model fields exhibit regionally distinct temporal variability, mostly determined by atmospheric forcing but in regions of significant sea-ice longer timescale variability is found. Some abrupt circulation changes accompany the relaxation of the westerlies following the peak North Atlantic Oscillation Index phase of the mid 1990s. The Greenland gyre spins up over the following years, with the increased circulation partially exiting through the Denmark Strait into the northern Atlantic as well as re-circulating within the Nordic Seas. This resulted in a distinct freshening around northern Iceland and an increase in the East Icelandic Current. However, these latter increases steadied after 1998, as the increased Greenland Sea gyre circulation led to a greater proportion of water leaving through the Denmark Strait, rather than re-circulating. The model Denmark Strait Outflow therefore doubles during the latter half of the 1990s. Increased convection in the Icelandic Sea in the model in 1998-2001 acted to obliterate the anomalies that would otherwise have fed into the East Icelandic Current. A fresh, cold anomaly from the Arctic during 1998/1999 is shown to propagate through the system. Model and observations show good agreement generally, but diverge at depth more in the last few years of the simulation. The model shows that density anomalies within the East Greenland Current do not exclusively derive from the Arctic but may also arise from air-sea interaction within the Greenland Sea. Convection is a major means of limiting anomaly propagation within the model. The contrast of climatological with daily forcing shows the inherent strength of the variability in the ocean circulation on sub-decadal timescales.     

On the relationship between spatial patterns of sea‐ice type and the mechanisms which create and maintain the North Water (NOW) polynya

Abstract

Polynyas represent polar oceanic areas with anomalous low sea‐ice concentrations. The North Water (NOW) Polynya refers to a region at the northern end of Baffin Bay which encompasses three separate polynyas. This paper examines the spatial patterns of sea‐ice cover within the NOW region during the winter, spring and fall of 1998 in the context of polynya formation and maintenance mechanisms. To accomplish this a sea‐ice classification scheme for RADARSAT‐1 ScanSAR imagery, obtained between 21 January and 7 December 1998, was developed and implemented within a Geographic Information System (GIS).

The results identify a clear and consistent spatial structure of sea‐ice cover throughout the winter, spring and fall of 1998. Temporally, the polynya opened southward along the Canadian coast and westward away from the Greenland coast. Comparison with parallel oceanographic, atmospheric and ice motion studies suggested that the polynya was primarily controlled by a latent heat mechanism with the exception of the west Greenland coast between Whale Sound and Cape York. The underlying mechanism used to explain the polynya's occurrence along this location is delayed ice formation during freeze‐up and a resultant thinner winter ice cover causing earlier spring ablation than surrounding areas. Arguments for oceanic and/or atmospheric sensible heat contributions are made.     

The role of salinity in the decadal variability of the North Atlantic meridional overturning circulation

An OGCM hindcast is used to investigate the linkages between North Atlantic Ocean salinity and circulation changes during 1963–2003. The focus is on the eastern subpolar region consisting of the Irminger Sea and the eastern North Atlantic where a careful assessment shows that the simulated interannual to decadal salinity changes in the upper 1,500 m reproduce well those derived from the available record of hydrographic measurements. In the model, the variability of the Atlantic meridional overturning circulation (MOC) is primarily driven by changes in deep water formation taking place in the Irminger Sea and, to a lesser extent, the Labrador Sea. Both are strongly influenced by the North Atlantic Oscillation (NAO). The modeled interannual to decadal salinity changes in the subpolar basins are mostly controlled by circulation-driven anomalies of freshwater flux convergence, although surface salinity restoring to climatology and other boundary fluxes each account for approximately 25% of the variance. The NAO plays an important role: a positive NAO phase is associated with increased precipitation, reduced northward salt transport by the wind-driven intergyre gyre, and increased southward flows of freshwater across the Greenland–Scotland ridge. Since the NAO largely controlled deep convection in the subpolar gyre, fresher waters are found near the sinking region during convective events. This markedly differs from the active influence on the MOC that salinity exerts at decadal and longer timescales in most coupled models. The intensification of the MOC that follows a positive NAO phase by about 2 years does not lead to an increase in the northward salt transport into the subpolar domain at low frequencies because it is cancelled by the concomitant intensification of the subpolar gyre which shifts the subpolar front eastward and reduces the northward salt transport by the North Atlantic Current waters. This differs again from most coupled models, where the gyre intensification precedes that of the MOC by several years.     

On the freshwater forcing and transport of the Atlantic thermohaline circulation

The 'conveyor belt' circulation of the Atlantic Ocean transports large amounts of heat northward, acting as a heating system for the northern North Atlantic region. It is widely thought that this circulation is driven by atmospheric freshwater export from the Atlantic catchment region, and that it transports freshwater northward to balance the loss to the atmosphere. Using results from a simple conceptual model and a global circulation model, it is argued here that the freshwater loss to the atmosphere arises mainly in the subtropical South Atlantic and is balanced by northward freshwater transport in the wind-driven subtropical gyre, while the thermohaline circulation transports freshwater southward. It is further argued that the direction of freshwater transport is closely linked to the dynamical regime and stability of the 'conveyor belt': if its freshwater transport is indeed southward, then its flow is purely thermally driven and inhibited by the freshwater forcing. In this case the circulation is not far from Stommel's saddle-node bifurcation, and a circulation state without NADW formation would also be stable. Received: 10 February 1996 / Accepted: 30 May 1996     

冬季格陵兰以东区域海冰与北太平洋风暴轴的关系

对45个冬季格陵兰以东区域海冰密集度场与北太平洋500 hPa位势高度滤波方差场作奇异值(SVD)分析.结果表明:SVD得到的第1对空间典型分布反映了冬季格陵兰以东区域海冰异常与北太平洋风暴轴异常变化密切相关.进一步的合成分析显示:海冰异常导致大气环流调整,气压梯度、急流、850 hPa天气尺度涡动热量经向通量和垂直通量、局地斜压性均发生改变,从而对北太平洋风暴轴的强度及中心位置位移造成影响.     

The North Atlantic thermohaline circulation simulated by the GISS climate model during 1970–99

Abstract

Evidence based on numerical simulations is presented for a strong correlation between the North Atlantic Oscillation (NAO) and the North Atlantic overturning circulation. Using an ensemble of numerical experiments with a coupled ocean‐atmosphere model including both natural and anthropogenic forcings, it is shown that the weakening of the thermohaline circulation (THC) could be delayed in response to a sustained upward trend in the NAO, which was observed over the last three decades of the twentieth century, 1970–99. Overall warming and enhanced horizontal transports of heat from the tropics to the subpolar North Atlantic overwhelm the NAO‐induced cooling of the upper ocean layers due to enhanced fluxes of latent and sensible heat, so that the net effect of warmed surface ocean temperatures acts to increase the vertical stability of the ocean column. However, the strong westerly winds cause increased evaporation from the ocean surface, which leads to a reduced fresh water flux over the western part of the North Atlantic. Horizontal poleward transport of salinity anomalies from the tropical Atlantic is the major contributor to the increasing salinities in the sinking regions of the North Atlantic. The effect of positive salinity anomalies on surface ocean density overrides the opposing effect of enhanced warming of the ocean surface, which causes an increase in surface density in the Labrador Sea and in the ocean area south of Greenland. The increased density of the upper ocean layer leads to deeper convection in the Labrador Sea and in the western North Atlantic. With a lag of four years, the meridional overturning circulation of the North Atlantic shows strengthening as it adjusts to positive density anomalies and enhanced vertical mixing. During the positive NAO trend, the salinity‐driven density instability in the upper ocean, due to both increased northward ocean transports of salinity and decreased atmospheric freshwater fluxes, results in a strengthening overturning circulation in the North Atlantic when the surface atmospheric temperature increases by 0.3°C and the ocean surface temperature warms by 0.5° to 1°C.     

春季格陵兰海冰与夏季中国气温和降水的关系

采有英国Hadley中心的GISST海冰面积资料，NCFP／NCAR再分析资料以及中国160站气温和降水资料，分析了春季格陵兰海冰面积与夏季中国区域气温和降水的关系。初步研究表明，春季格陵兰海冰面积变化和随后夏季我国黄河长江中下游之间地区气温以及8月份华北和西南地区降水呈明显正相关，而和6月黄河中上游地区降水则具有明显的负相关。同时，春季格陵兰海冰异常时期对应着北半球大气环流的明显主为化，表明海冰与我国气温及降水之间的联系具有一定的环流背景。     

On the interannual variability of precipitation and runoff in the Mackenzie drainage basin

An analysis is presented of extratropical cyclone frequency, the 500 hPa height standard deviation field and the monthly 700 hPa height field in the Northern Hemisphere, together with precipitation in the Mackenzie basin and the Mackenzie River runoff. Spatial and temporal variability in the data are examined for the period 1965 to 1989, and a cross-correlation analyses is performed to determine the relationship between the runoff and the precipitation variations, and between the precipitation and the atmospheric circulation anomalies. It is found that precipitation fluctuations in the Mackenzie River drainage basin are strongly linked to variations in the Mackenzie River runoff and in the North Pacific storm tracks, with the time scale of variability ranging from interannual to decadal. The results are discussed in relation to the interdecadal Arctic climate cycle proposed by Mysak, Manak and Marsden, and revised by Mysak and Power. In particular, the latter authors hypothesized that, as part of this cycle, air-sea interactions and synoptic scale processes over the northwestern North Atlantic influenced, via cyclone movements in the Labrador Sea and Baffin Bay, precipitation in northern Canada and hence river runoff into the Arctic. The results of this study indicate that such influences on the precipitation in the Mackenzie basin are small, and hence that the Mysak-Power feedback loop which describes this climate cycle needs further revision.     

Variability of Sea-Ice Extent in Baffin Bay over the Last Millennium

Comparison of an ice core glaciochemical time-series developed from thePenny Ice Cap (PIC), Baffin Island and monthly sea-ice extent reveals astatisticallysignificant inverse relationship between changes in Baffin Bay spring sea-iceextent andPenny Ice Cap sea-salt concentrations for the period 1901–1990 AD.Empiricalorthogonal function analysis demonstrates the joint behavior between changesin PICsea-salt concentrations, sea-ice extent, and changes in North Atlanticatmosphericcirculation. Our results suggest that sea-salt concentrations in snowpreserved on thePIC reflect local to regional springtime sea-ice coverage. The PIC sea-saltrecord/sea-ice relationship is further supported by decadal and century scalecomparisonwith other paleoclimate records of eastern Arctic climate change over the last700 years. Our sea-salt record suggests that, while the turn of the century wascharacterized bygenerally milder sea-ice conditions in Baffin Bay, the last few decades ofsea-ice extentlie within Little Ice Age variability and correspond to instrumental recordsof lowertemperatures in the Eastern Canadian Arctic over the past three decades.