Description: Five years of oxygen isotope and hydrological surveys reveal interannual variations in the inventory and distribution of river water over the Laptev Sea. In 2007, 2009, and 2010 relatively low amounts of river water (≤1500 km3) were found and were mostly located in the southeastern Laptev Sea. In 2008 and 2011, high amounts of river water (~1600 km3 and ~2000 km3) were found, especially in the central and northern part of the shelf, suggesting a northward export of this water. This temporal pattern is coherent with the summer Arctic Dipole index that was higher in 2008 and 2011. Our results suggest that the Arctic Dipole might influence the export of river water from the Laptev Sea. Moreover, the river water inventory in the Laptev Sea seems related to the freshwater content of the Arctic Ocean with a 2 years lag.

Description: Over the last several decades, the Arctic and North Atlantic have undergone substantial changes. Enhanced transport of warmer air from lower latitudes led to increased arctic surface air temperature associated with decreased arctic sea-level pressure and increased polar atmospheric cyclonicity which led to reductions in arctic ice extent and a decrease of ice thickness. Changes in the Arctic Ocean are also significant. Positive temperature anomalies in the intermediate Atlantic Water (AW) layer of the Arctic Ocean were found in the 1990s and 2000s. Freshwater content in the upper layer of the Arctic Ocean was also reduced dramatically over the recent decades. Concurrent with these high-latitude changes are North Atlantic warming and salinification in the upper 300 m layer (except the subpolar North Atlantic) and widespread cooling and freshening in the 1000-3000 m layer. We suggest that both long-term climate trend and low-frequency variability play a substantial role in shaping these recent changes in the Arctic/North Atlantic climate system. Understanding the key factors influencing the Arctic/North Atlantic multi-decadal variability may provide a reasonable means for developing climatic forecasts of widespread persistent anomalies. Xiangdong

Description: Due to hydrostatic imbalance, water from the North Pacific flows through the Bering Strait, transits the upper levels of the Arctic Ocean, and finds its way to the North Atlantic. Waters recently originating from the North Pacific generally have a distinct temperature, salinity, and silicate signature. Summer and winter modification produces two forms of Pacific-origin water that comprise the upper and middle halocline of the upper layer, respectively. Using hydrographic and hydrochemical data (1950 - 1993), annual wintertime fields are estimated and used to delineate the boundary between the halocline of predominately Atlantic Water from the halocline of predominately Pacific Water. The horizontal extent of Pacific Winter Water is often sharply defined by a strong gradient in silicate. Examinations of the hydrographic/hydrochemical fields also suggest that temperature on the 33.1 psu isopycnal can also be used to estimate the boundary between halocline waters. We determined that the boundary lies at the intersection of 33.1 psu isohaline and -1.6oC isotherm. The interannual and decadal positions of the boundary are illustrated. Finally, we show data of the vertical and horizontal structure of the interface between the two haloclines. During summer and early fall, much of the Chukchi Shelf is ice free and surface waters are found to be several degrees above the freezing temperatures. This warm water flows off the shelf and subsides beneath the fresher surface water of the Canadian Basin. In subsequent winters, remnants of this warm shelf water can be identified by a slight temperature maximum, greater than -1.4oC, in the upper halocline. Data collected during the “Sever” (and other) expeditions are analyzed to determine the extent of this Pacific Summer Water (PSW). Annual spatial patterns of maximum temperature and thickness of the PSW are shown for selected years. Summaries of volume and heat content are estimated. The transport of PSW is reconciled with patterns of geostrophiclly balanced flow in the upper halocline off the Beaufort and Chukchi Seas. We show time series of water volume and heat content of PSW with comparison to indexes of atmospheric circulation. Finally, we calculated the circulation of Pacific Water in the Arctic Ocean based on a model of Bernoulli equations.

Description: Combined salinity and δ18O data from summer 2007 reveal a significant change in brine production in the Laptev Sea relative to summer 1994. The distribution of river water and brine enriched waters on the Laptev Sea shelf is derived based on mass balance calculations using salinity and δ18O data. While in 1994 maximal influence of brines is seen within bottom waters [Bauch et al., 2009a], in 2007 the influence of brines is highest within the surface layer and only a moderate influence of brines is observed in the bottom layer. In contrast to 2007, salinity and δ18O data from summer 1994 clearly identify a locally formed brine enriched bottom water mass as mixing endmember between surface layer and inner shelf waters on one side and with higher salinity water from the outer Laptev Sea on the other side. In 2007 the brine enriched waters are predominantly part of the surface regime and the mixing endmember between surface layer and outer shelf waters is replaced by a relatively salty bottom water mass. This relatively salty bottom water probably originates from the western Laptev Sea. The inverted distribution of brines in the water column in 2007 relative to 1994 suggests a less effective winter sea-ice formation in winter 2006/2007 combined with advection of more saline waters from the western Laptev Sea or the outer shelf precedent to 1 the climatically extreme summer 2007. The observed changes result in an altered export of waters from the Laptev Sea to the Arctic Ocean halocline.

Description: Sediment transport dynamics were studied during ice-free conditions under different atmospheric circulation regimes on the Laptev Sea shelf (Siberian Arctic). To study the interannual variability of suspended particulate matter (SPM) dynamics and their coupling with the variability in surface river water distribution on the Laptev Sea shelf, detailed oceanographic, optical (turbidity and Ocean Color satellite data), and hydrochemical (nutrients, SPM, stable oxygen isotopes) process studies were carried out continuously during the summers of 2007 and 2008. Thus, for the first time SPM and nutrient variations on the Laptev Sea shelf under different atmospheric forcing and the implications for the turbidity and transparency of the water column can be presented. The data indicate a clear link between different surface distributions of riverine waters and the SPM transport dynamics within the entire water column. The summer of 2007 was dominated by shoreward winds and an eastward transport of riverine surface waters. The surface SPM concentration on the southeastern inner shelf was elevated, which led to decreased transmissivity and increased light absorption. Surface SPM concentrations in the central and northern Laptev Sea were comparatively low. However, the SPM transport and concentration within the bottom nepheloid layer increased considerably on the entire eastern shelf. The summer of 2008 was dominated by offshore winds and northward transport of the river plume. The surface SPM transport was enhanced and extended onto the mid-shelf, whereas the bottom SPM transport and concentration was diminished. This study suggests that the SPM concentration and transport, in both the surface and bottom nepheloid layers, are associated with the distribution of riverine surface waters which are linked to the atmospheric circulation patterns over the Laptev Sea and the adjacent Arctic Ocean during the open water season. A continuing trend toward shoreward winds, weaker stratification and higher SPM concentration throughout the water column might have severe consequences for the ecosystem on the Laptev Sea shelf.

Description: The thermohaline structure of the Arctic Basin (AB) of the Arctic Ocean (AO) is determined to a great extent by an intermediate water layer existing under ice at a depth varying from 100 to 700–1000 m. The water layer is formed by warm North Atlantic Water (AW), which enters the AB by two ways: through Fram Strait and the Barents Sea (Fig. 1). The AW arriving to the AB via Fram Strait extends further eastward along the continental slope of the Eurasian Arctic region and forms the Fram Branch (FBAW). The Barents Branch of the AW (BBAW) was formed by the North Atlantic Water entering the Barents Sea between the Spitsbergen Archipelago and the Scandinavian Peninsula. Both branches merge in the northern Kara Sea.

Description: Recent observations show dramatic changes of the Arctic atmosphere–ice–ocean system. Here the authors demonstrate, through the analysis of a vast collection of previously unsynthesized observational data, that over the twentieth century the central Arctic Ocean became increasingly saltier with a rate of freshwater loss of 239 ± 270 km3 decade−1. In contrast, long-term (1920–2003) freshwater content (FWC) trends over the Siberian shelf show a general freshening tendency with a rate of 29 ± 50 km3 decade−1. These FWC trends are modulated by strong multidecadal variability with sustained and widespread patterns. Associated with this variability, the FWC record shows two periods in the 1920s–30s and in recent decades when the central Arctic Ocean was saltier, and two periods in the earlier century and in the 1940s–70s when it was fresher. The current analysis of potential causes for the recent central Arctic Ocean salinification suggests that the FWC anomalies generated on Arctic shelves (including anomalies resulting from river discharge inputs) and those caused by net atmospheric precipitation were too small to trigger long-term FWC variations in the central Arctic Ocean; to the contrary, they tend to moderate the observed long-term central-basin FWC changes. Variability of the intermediate Atlantic Water did not have apparent impact on changes of the upper–Arctic Ocean water masses. The authors’ estimates suggest that ice production and sustained draining of freshwater from the Arctic Ocean in response to winds are the key contributors to the salinification of the upper Arctic Ocean over recent decades. Strength of the export of Arctic ice and water controls the supply of Arctic freshwater to subpolar basins while the intensity of the Arctic Ocean FWC anomalies is of less importance. Observational data demonstrate striking coherent long-term variations of the key Arctic climate parameters and strong coupling of long-term changes in the Arctic–North Atlantic climate system. Finally, since the high-latitude freshwater plays a crucial role in establishing and regulating global thermohaline circulation, the long-term variations of the freshwater content discussed here should be considered when assessing climate change and variability.

Description: Highlights • Atlantic Water modified by sea-ice melt and meteoric water at Barents Sea slope • LHW may be divided into different types by Principal Component Analysis (PCA) • high salinity LHW-type forms in the Barents and Kara seas • low salinity LHW-types form in the western Laptev Sea or enter via Vilkitsky Strait • PCA does not support a distinction between onshore and offshore LHW branches Abstract Salinity and stable oxygen isotope (δ18O) evidence shows a modification of Atlantic Water in the Arctic Ocean by a mixture of sea-ice meltwater and meteoric waters along the Barents Sea continental margin. On average no further influence of meteoric waters is detectable within the core of the Atlantic Water east of the Kara Sea as indicated by constant δ18O, while salinity further decreases along the Siberian continental slope. Lower halocline waters (LHW) may be divided into different types by Principal Component Analysis. All LHW types show the addition of river water and an influence of sea-ice formation to a varying extent. The geographical distribution of LHW types suggest that the high salinity type of LHW forms in the Barents and Kara seas, while other LHW types are formed either in the northwestern Laptev Sea or from southeastern Kara Sea waters that enter the northwestern Laptev Sea through Vilkitsky Strait. No further modification of LHW is seen in the eastern Laptev Sea but the distribution of LHW-types suggest a bifurcation of LHW at this location, possibly with one branch continuing along the continental margin and a second branch along the Lomonosov Ridge. We see no pronounced distinction between onshore and offshore LHW types, as the LHW components that are found within the halocline over the basin also show a narrow bottom-bound distribution at the continental slope that is consistent with a shelf boundary current as well as a jet of water entering the western Laptev Sea from the Kara Sea through Vilkitsky Strait.