Genrikh Alekseev

Variability and Trends of Air Temperature and Pressure in the Maritime Arctic, 1875–2000

Arctic atmospheric variability during the industrial era (1875‐2000) is assessed using spatially averaged surface air temperature (SAT) and sea level pressure (SLP) records. Air temperature and pressure display strong multidecadal variability on timescales of 50‐80 yr [termed low-frequency oscillation (LFO)]. Associated with this variability, the Arctic SAT record shows two maxima: in the 1930s‐40s and in recent decades, with two colder periods in between. In contrast to the global and hemispheric temperature, the maritime Arctic temperature was higher in the late 1930s through the early 1940s than in the 1990s. Incomplete sampling of large-amplitude multidecadal fluctuations results in oscillatory Arctic SAT trends. For example, the Arctic SAT trend since 1875 is 0.09 6 0.038C decade21, with stronger spring- and wintertime warming; during the twentieth century (when positive and negative phases of the LFO nearly offset each other) the Arctic temperature increase is 0.05 6 0.048C decade21, similar to the Northern Hemispheric trend (0.068C decade21). Thus, the large-amplitude multidecadal climate variability impacting the maritime Arctic may confound the detection of the true underlying climate trend over the past century. LFO-modulated trends for short records are not indicative of the long-term behavior of the Arctic climate system. The accelerated warming and a shift of the atmospheric pressure pattern from anticyclonic to cyclonic in recent decades can be attributed to a positive LFO phase. It is speculated that this LFO-driven shift was crucial to the recent reduction in Arctic ice cover. Joint examination of air temperature and pressure records suggests that peaks in temperature associated with the LFO follow pressure minima after 5‐15 yr. Elucidating the mechanisms behind this relationship will be critical to understanding the complex nature of low-frequency variability.

Variability of the intermediate Atlantic water of the Arctic Ocean over the last 100 years

Recent observations show dramatic changes of the Arctic atmosphere‐ice‐ocean system, including a rapid warming in the intermediate Atlantic water of the Arctic Ocean. Here it is demonstrated through the analysis of a vast collection of previously unsynthesized observational data, that over the twentieth century Atlantic water variability was dominated by low-frequency oscillations (LFO) on time scales of 50‐80 yr. Associated with this variability, the Atlantic water temperature record shows two warm periods in the 1930s‐40s and in recent decades and two cold periods earlier in the century and in the 1960s‐70s. Over recent decades, the data show a warming and salinification of the Atlantic layer accompanied by its shoaling and, probably, thinning. The estimate of the Atlantic water temperature variability shows a general warming trend; however, over the 100-yr record there are periods (including the recent decades) with short-term trends strongly amplified by multidecadal variations. Observational data provide evidence that Atlantic water temperature, Arctic surface air temperature, and ice extent and fast ice thickness in the Siberian marginal seas display coherent LFO. The hydrographic data used support a negative feedback mechanism through which changes of density act to moderate the inflow of Atlantic water to the Arctic Ocean, consistent with the decrease of positive Atlantic water temperature anomalies in the late 1990s. The sustained Atlantic water temperature and salinity anomalies in the Arctic Ocean are associated with hydrographic anomalies of the same sign in the Greenland‐Norwegian Seas and of the opposite sign in the Labrador Sea. Finally, it is found that the Arctic air‐sea‐ice system and the North Atlantic sea surface temperature display coherent low-frequency fluctuations. Elucidating the mechanisms behind this relationship will be critical to an understanding of the complex nature of low-frequency variability found in the Arctic and in lower-latitude regions.

Long-Term Ice Variability in Arctic Marginal Seas

Abstract Examination of records of fast ice thickness (1936–2000) and ice extent (1900–2000) in the Kara, Laptev, East Siberian, and Chukchi Seas provide evidence that long-term ice thickness and extent trends are small and generally not statistically significant, while trends for shorter records are not indicative of the long-term tendencies due to large-amplitude low-frequency variability. The ice variability in these seas is dominated by a multidecadal, low-frequency oscillation (LFO) and (to a lesser degree) by higher-frequency decadal fluctuations. The LFO signal decays eastward from the Kara Sea where it is strongest. In the Chukchi Sea ice variability is dominated by decadal fluctuations, and there is no evidence of the LFO. This spatial pattern is consistent with the air temperature–North Atlantic Oscillation (NAO) index correlation pattern, with maximum correlation in the near-Atlantic region, which decays toward the North Pacific. Sensitivity analysis shows that dynamical forcing (wind or surfac...

Arctic Sea Ice Data Sets in the Context of Climate Change During the 20th Century

Available estimates of sea ice extent in the northern hemisphere cover the period from the early part of the 20th century to present day. We analyze changes in ice extent and thickness in the Arctic and its relation to surface air temperature over this period. Time series obtained from different data sets demonstrate better agreement after the 1950s and especially since 1979 with the onset of regular remote sensing observations from satellites. Statistics of time series show minima ice extent in August–September. Mean square deviations reach maxima in July–August. The distributions of trend coefficients show a more significant decrease of summer ice extent. Statistics of monthly ice extent in the Siberian Arctic seas show a similar distribution. September ice extent in the majority of the Siberian Arctic seas and in the Barents Sea reveal rapid shrinking during Arctic warmings in the 1920–1940s and 1990s. Significant correlation between surface air temperature and ice extent occurs in summer months with maximum in June under the influence of June maximum solar irradiation, and amplified by heat advection in the atmosphere and ice extent anomalies in the previous months. The relationship between variations of winter air temperature and ice extent is weaker because winter ice extent anomalies depend on air temperature anomalies as well as on the area occupied by a freshened upper layer. Good agreement between variations of the sum of summer air temperature in the marine Arctic and sea ice extent in September is found (correlation coefficient is 0.85). It confirms that summer melting plays the most important role in the sea ice volume decrease. The renewed observations in 2004–2005 at the Russian “North Pole” drifting stations revealed that the area-averaged perennial ice in the Arctic Basin decreased by 110cm relative to the 1990 value. But the land-fast ice thickness in the Kara and Laptev Seas show an insignificant positive linear trend for 1934–2005 in agreement with the sum of winter air temperature. The negative trend of land-fast ice thickness becomes apparent starting from the 1970s.

The influence of the North Atlantic on climate variations in the Barents Sea and their predictability

The effects of Atlantic water inflow on the climate variability in the Barents Sea are studied. Initial data are the series of water temperature at the Kola meridian cross-section, monthly values of ice extent, air temperature at the stations, sea level pressure from the reanalysis data, and sea surface temperature. The methods of multivariate correlation, spectral, and factor analysis and EOF decomposition are used. It was found that variations in the Atlantic water inflow define the main part of interannual variability of sea ice extent, water temperature, and air temperature in the Barents Sea in the cold season. The influence of regional atmospheric circulation on the interannual variability of these parameters is small. The effects that water temperature anomalies in the area of Newfoundland and in the equatorial part of the North Atlantic have on climate parameters in the Barents Sea are discovered. The response of these parameters lags behind the respective anomalies by 9-58 months. The high correlation between them makes it possible to develop the method of statistical forecasting of sea ice extent and water temperature in the Barents Sea with the lead time up to 4 years.

Arctic sea ice cover in connection with climate change

Recently published studies on key issues in the evolution of Arctic sea ice cover are reviewed and attempts to answer disputable questions are made in the research part of the work. It is shown that climate warming, manifested in an increase in the surface air temperature, and reduction in the ice cover develop with a high degree of agreement in summer. Based on this fact, anomalies of the September ice-cover area have been retrieved from 1900. They show a significant decrease in the 1930–1940s, which is almost twice as low as in 2007–2012. The influence of fluctuations in the flow of warm and salty Atlantic water is noted in variations in the winter maximum of the ice-cover area in the Barents Sea. An accelerated positive trend has been ascertained for the air temperature in late autumn–early winter in 1993–2012 due to an increase in the open water area in late summer. Inherent regularities of the ice-cover-area variability made it possible to develop a prediction of the monthly values of sea-ice extent with a head time from 6 months to 2 years. Their strong correlation with summer air temperature is used to estimate the onset of summer ice clearance in the Arctic.

Heat, salt, and volume transports in the eastern Eurasian Basin ofthe Arctic Ocean, from two years of mooring observations

Abstract. This study discusses along-slope volume, heat, and salt transports derived from observations collected in 2013–15 using a cross-slope array of six moorings ranging from 250 m to 3900 m in the eastern Eurasian Basin (EB) of the Arctic Ocean. These observations demonstrate that in the upper 780 m layer, the along-slope boundary current advected, on average, 5.1 ± 0.1 Sv of water, predominantly in the eastward (shallow-to-right) direction. Monthly net volume transports across the Laptev Sea slope vary widely, from ~ 0.3 ± 0.8 in April 2014 to ~ 9.9 ± 0.8 Sv in June 2014. 3.1 ± 0.1 Sv (or 60 %) of the net transport was associated with warm and salty intermediate-depth Atlantic Water (AW). Calculated heat transport for 2013–15 (relative to −1.8 °C) was 46.0 ± 1.7 TW, and net salt transport (relative to zero salinity) was 172 ± 6 Mkg/s. Estimates for AW heat and salt transports were 32.7 ± 1.3 TW (71 % of net heat transport) and 112 ± 4 Mkg/s (65 % of net salt transport). The variability of currents explains ~ 90 % of the variability of the heat and salt transports. The remaining ~ 10 % is controlled by temperature and salinity anomalies together with temporal variability of the AW layer thickness. The annual mean volume transports decreased by 25 % from 5.8 ± 0.2 Sv in 2013–14 to 4.4 ± 0.2 Sv in 2014–15 suggesting that changes of the transports at interannual and longer time scales in the eastern EB may be significant.

Interaction with the Global Climate System

The Arctic is part of the global climate system. To address the issue of climate, the fluxes of heat, salt, and fresh water must be considered. One of the most speculated reasons for rapid climate change in the subarctic North Atlantic, and the global conveyor belt, is a breakdown of the thermohaline circulation (THC) due to an increased fresh water supply. Whitehead’s (Estuaries 21:281–293, 1998) one-box dynamic model is used to show how multiple states and catastrophe can occur in the Arctic Mediterranean with variable freshening and cooling. The broader question is how this interacts with the global climate. In this chapter, we focus on the oceanic aspects of the arctic climate system, discuss processes, review the data, and speculate on the role this part of the globe has in the greater context of global climate. The interaction with the global system comprises the outflow of freshwater and ice, and deeper, freshened, and cooled seawater into the subarctic North Atlantic, via the Labrador Sea. An example of significant climate variability in the twentieth century is presented.