ALBERT

Description: The Weddell Sea plays an important role for the global oceans and climate by being one of the biggest production and export areas of Antarctic Bottom Water (AABW). Circumpolar Deep Water (CDW) enters the Weddell Gyre (WG) at its eastern boundary. Then called Warm Deep Water (WDW), it is a major contributor to the formation of deep and bottom waters due to ocean-ice shelf interactions in the southern and soutwestern Weddell Sea. Hydrographic data collected between 0 and 30°E on the RV Polarstern cruise ANT XX/2 reveals a two-core structure for the eastern inflow of warm water at roughly 20°E but not further downstream at the Greenwich meridian (GM). Model results and climatological fields suggest that the two cores represent two separate modes of warm inflow. One mode is driven by eddy mixing in the northeastern corner of the WG and the other one is an advective mode, forming the southern branch of the inflow which extends beyond 30°E before turning westward. Both pathways are likely to carry waters from different origins within the Antarctic Circumpolar Current (ACC), where more ventilated CDW is found at the Southern Boundary (SB) compared to the centre. The southern route shows considerable interannual variability in the model. A variable inflow of two types of CDW together with admixed recirculated and cooler waters from the Weddell Sea can potentially contribute to the observed variability and warming trend of WDW over the last decade at the GM.

Description: Microcystis are known for their potential ability to synthesize toxins, mainly microcystins (MCs). In order to evaluate the effects of temperature on chlorophyll a (Chl a), growth, physiological responses and toxin production of a native Microcystis aeruginosa, we exposed the cells to low (23 °C) and high (29 °C) temperature in addition to a 26 °C control treatment. Exponential growth rate was significantly higher at 29 °C compared to 23 °C and control, reaching 0.43, 0.32 and 0.33 day−1 respectively. In addition, there was a delay of the start of exponential growth at 23 °C. However, the intracellular concentration of Chl a decreased significantly due to temperature change. A significant increase in intracellular ROS was observed in coincidence with the activation of enzymatic antioxidant catalase (CAT) during the first two days of exposure to 23° and 29 °C in comparison to the control experiment, decreasing thereafter to nearly initial values. Five MCs were determined by LC-MS/MS analysis. In the experiments, the highest MC concentration, 205 fg [Leu1] MC-LR.cell− 1 expressed as MC-LR equivalent was measured in the beginning of the experiment and subsequently declined to 160 fg.cell− 1 on day 2 and 70 fg.cell− 1 on day 4 in cells exposed to 29 °C. The same trend was observed for all other MCs except for the least abundant MC-LR which showed a continuous increase during exposure time. Our results suggest a high ability of M. aeruginosa to perceive ROS and to rapidly initiate antioxidant defenses with a differential response on MC production.

Description: Over the past ~ 5000 years, amplified dust generation and deposition in the American West has been linked to human activity. In recent decades, intensified rates of agriculture and livestock grazing have been correlated with greater dust production detected on seasonal to annual timescales. The combination of land use intensification and climate change (i.e. increased drought frequency) in North America highlights the importance of characterizing the sources of dust both before and after the influence of anthropogenic activity. We apply high-precision geochemical and isotopic (Sr and Nd isotopes) techniques to an ice core from the Upper Fremont Glacier (Wyoming, USA) to produce the first glacial dataset from the American West. Our Sr-Nd isotopic composition data indicates the evolving dust provenance to the Upper Fremont Glacier (UFG) from a long-range transport of mineral dust to a local source. This increasing input of dust from a local source is supported by a rise in average dust particle diameter combined with greater average dust concentration throughout the record. The greater presence of dust particles smaller than 2.5 μm in the most recent samples from UFG ice core record support existing satellite and sediment core data regarding the effects of anthropogenic activity upon dust sources and pathways in the American West. Although the Sr-Nd isotope database in North America needs be expanded, our results provide a survey of windborne dust through the past 270 years.

Description: Reactive iron (oxyhydr)oxide minerals preferentially undergo early diagenetic redox cycling which can result in the production of dissolved Fe(II), the adsorption of Fe(II) onto particle surfaces, and the formation of authigenic Fe minerals. The partitioning of iron in sediments has traditionally been studied by applying sequential extractions that target operationally-defined iron phases. Here, we complement an existing sequential leaching method by developing a sample processing protocol for δ56Fe analysis, which we subsequently use to study Fe phase-specific fractionation related to dissimilatory iron reduction in a modern marine sediment. Carbonate-Fe was extracted by acetate, easily reducible oxides (e.g. ferrihydrite and lepidocrocite) by hydroxylamine–HCl, reducible oxides (e.g. goethite and hematite) by dithionite–citrate, and magnetite by ammonium oxalate. Subsequently, the samples were repeatedly oxidized, heated and purified via Fe precipitation and column chromatography. The method was applied to surface sediments collected from the North Sea, south of the island of Helgoland. The acetate-soluble fraction (targeting siderite and ankerite) showed a pronounced downcore δ56Fe trend. This iron pool was most depleted in 56Fe close to the sediment–water interface, similar to trends observed for pore-water Fe(II). We interpret this pool as surface-reduced Fe(II), rather than siderite or ankerite, that was open to electron and atom exchange with the oxide surface. Common extractions using 0.5 M HCl or Na-dithionite alone may not resolve such trends, as they dissolve iron from isotopically distinct pools leading to a mixed signal. Na-dithionite leaching alone, for example, targets the sum of reducible Fe oxides that potentially differ in their isotopic fingerprint. Hence, the development of a sequential extraction Fe isotope protocol provides a new opportunity for detailed study of the behavior of iron in a wide range of environmental settings.

Description: The focus of this research has been on detecting changes in lake areas, vegetation, land surface temperatures, and the area covered by snow, using data from remote sensing. The study area covers the main (central) part of the Lena River catchment in the Yakutia region of Siberia (Russia), extending from east of Yakutsk to the central Siberian Plateau, and from the southern Lena River to north of the Vilyui River. Approximately 90% of the area is underlain by continuous permafrost. Remote sensing products were used to analyze changes in water bodies, land surface temperature (LST), and leaf area index (LAI), as well as the occurrence and extent of forest fires, and the area and duration of snow cover. The remote sensing analyses (for LST, snow cover, LAI, and fire) were based on MODIS–derived NASA products (250–1000 m) for 2000 to 2011. Changes in water bodies were calculated from two mosaics of (USGS) Landsat (30 m) satellite images from 2002 and 2009. Within the study area's 315,000 km2 the total area covered by lakes increased by 17.9% between 2002 and 2009, but this increase varied in different parts of the study area, ranging between 11% and 42%. The land surface temperatures showed a consistent warming trend, with an average increase of about 0.12 °C/year. The average rate of warming during the April–May transition period was 0.17 °C/year and 0.19 °C/year in the September–October period, but ranged up to 0.49 °C/year during September–October. Regional differences in the rates of land surface temperature change, and possible reasons for the temperature changes, are discussed with respect to changes in the land cover. Our analysis of a broad spectrum of variables over the study area suggests that the spring warming trend is very likely to be due to changes in the area covered by snow. The warming trend observed in fall does not, however, appear to be directly related to any changes in the area of snow cover, or to the atmospheric conditions, or to the proportion of the land surface that is covered by water (i.e., to wetting and drying). Supplementary data (original data, digitized version of the maps, metadata) are archived under PANGAEA (http://dx.doi.org/10.1594/PANGAEA.855124).

Description: The Southern Ocean (SO) is a major sink for anthropogenic atmospheric carbon dioxide (CO2), potentially harbouring even greater potential for additional sequestration of CO2 through enhanced phytoplankton productivity. In the SO, primary productivity is primarily driven by bottom up processes (physical and chemical conditions) which are spatially and temporally heterogeneous. Due to a paucity of trace metals (such as iron) and high variability in light, much of the SO is characterised by an ecological paradox of high macronutrient concentrations yet uncharacteristically low chlorophyll concentrations. It is expected that with increased anthropogenic CO2 emissions and the coincident warming, the major physical and chemical process that govern the SO will alter, influencing the biological capacity and functioning of the ecosystem. This review focuses on the SO primary producers and the bottom up processes that underpin their health and productivity. It looks at the major physico-chemical drivers of change in the SO, and based on current physiological knowledge, explores how these changes will likely manifest in phytoplankton, specifically, what are the physiological changes and floristic shifts that are likely to ensue and how this may translate into changes in the carbon sink capacity, net primary productivity and functionality of the SO.

Description: We compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub-polar marine ecosystems. Circulation patterns differ strikingly between the north and south. Meridional circulation in the north provides connections between the sub-Arctic and Arctic despite the presence of encircling continental landmasses, whereas annular circulation patterns in the south tend to isolate Antarctic surface waters from those in the north. These differences influence fundamental aspects of the polar ecosystems from the amount, thickness and duration of sea ice, to the types of organisms, and the ecology of zooplankton, fish, seabirds and marine mammals. Meridional flows in both the North Pacific and the North Atlantic oceans transport heat, nutrients, and plankton northward into the Chukchi Sea, the Barents Sea, and the seas off the west coast of Greenland. In the North Atlantic, the advected heat warms the waters of the southern Barents Sea and, with advected nutrients and plankton, supports immense biomasses of fish, seabirds and marine mammals. On the Pacific side of the Arctic, cold waters flowing northward across the northern Bering and Chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there. Southward flow of cold Arctic waters into sub-Arctic regions of the North Atlantic occurs mainly through Fram Strait with less through the Barents Sea and the Canadian Archipelago. In the Pacific, the transport of Arctic waters and plankton southward through Bering Strait is minimal. In the Southern Ocean, the Antarctic Circumpolar Current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub-Antarctic waters, with the consequent evolution of Antarctic zooplankton and fish species largely occurring in isolation from those to the north. The Antarctic Circumpolar Current also disperses biota throughout the Southern Ocean, and as a result, the biota tends to be similar within a given broad latitudinal band. South of the Southern Boundary of the ACC, there is a large-scale divergence that brings nutrient-rich water to the surface. This divergence, along with more localized upwelling regions and deep vertical convection in winter, generates elevated nutrient levels throughout the Antarctic at the end of austral winter. However, such elevated nutrient levels do not support elevated phytoplankton productivity through the entire Southern Ocean, as iron concentrations are rapidly removed to limiting levels by spring blooms in deep waters. However, coastal regions, with the upward mixing of iron, maintain greatly enhanced rates of production, especially in coastal polynyas. In these coastal areas, elevated primary production supports large biomasses of zooplankton, fish, seabirds, and mammals. As climate warming affects these advective processes and their heat content, there will likely be major changes in the distribution and abundance of polar biota, in particular the biota dependent on sea ice.