Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO2 levels

A large-scale multidisciplinary mesocosm experiment in an Arctic fjord (Kongsfjorden, Svalbard; 78°56.2′N) was used to study Arctic marine food webs and biogeochemical elements cycling at natural and elevated future carbon dioxide (CO2) levels. At the start of the experiment, marine-derived chromophoric dissolved organic matter (CDOM) dominated the CDOM pool. Thus, this experiment constituted a convenient case to study production of autochthonous CDOM, which is typically masked by high levels of CDOM of terrestrial origin in the Arctic Ocean proper. CDOM accumulated during the experiment in line with an increase in bacterial abundance; however, no response was observed to increased pCO2 levels. Changes in CDOM absorption spectral slopes indicate that bacteria were most likely responsible for the observed CDOM dynamics. Distinct absorption peaks (at ~ 330 and ~ 360 nm) were likely associated with mycosporine-like amino acids (MAAs). Due to the experimental setup, MAAs were produced in absence of ultraviolet exposure providing evidence for MAAs to be considered as multipurpose metabolites rather than simple photoprotective compounds. We showed that a small increase in CDOM during the experiment made it a major contributor to total absorption in a range of photosynthetically active radiation (PAR, 400-700 nm) and, therefore, is important for spectral light availability and may be important for photosynthesis and phytoplankton groups composition in a rapidly changing Arctic marine ecosystem

Sea ice CO2 flux in the Southern Ocean during mid-winter and early spring

There seems little doubt that sea ice is permeable to CO2 and other gases although air–sea ice gas flux is more or less inhibited at a brine volume fraction of less than 5% representing the threshold for fluid permeability of sea ice. Generally, air–sea ice CO2 flux is at its minimum in winter due to low sea ice temperatures and consequently reduced permeability despite the fact the partial pressure of CO2 in sea ice is usually high at that time and sea ice has therefore the potential to release CO2 to the atmosphere. Here, we present first evidence that snow laden Antarctic sea ice can act as source for atmospheric CO2 even during mid-winter and early spring. During a mid-winter cruise to the Weddell Sea (AWECS, 2013) and an early spring cruise off east Antarctica (SIPEX-2, 2012), due to thick insulating snow covers, the bottom of the snow and the surface of the sea ice were relatively warm (>–10°C) even though air temperature was sometimes below –30°C. In addition, in both areas, sea ice was characterized by high bulk-salinities, resulting in brine volume fractions that are generally higher than 5%. Automatic “open-closed” chamber measurements indicated positive CO2 fluxes of up to +2.5 mmol C m–2 day–1, illustrating that sea ice acted as a source of atmospheric CO2. Higher fluxes were measured at bare ice surfaces after removing the snow. However, generally low snow densities (mean: 339 kg m–3), indicating a permeable snow cover, facilitated degassing of CO2 at the snow-air interface. Our results therefore suggest that even in the winter and early spring, Antarctic sea ice can act as CO2 source for the atmosphere, particularly in areas with a thick insulating snow cover.Bigsout

Characteristics of colored dissolved organic matter (CDOM) in the Arctic outflow in Fram Strait: assessing the changes and fate of terrigenous CDOM in the Arctic Ocean

Absorption coefficients of colored dissolved organic matter (CDOM) were measured together with salinity, delta O-18, and inorganic nutrients across the Fram Strait. A pronounced CDOM absorption maximum between 30 and 120 m depth was associated with river and sea ice brine enriched water, characteristic of the Arctic mixed layer and upper halocline waters in the East Greenland Current (EGC). The lowest CDOM concentrations were found in the Atlantic inflow. We show that the salinity-CDOM relationship is not suitable for evaluating conservative mixing of CDOM. The strong correlation between meteoric water and CDOM is indicative of the riverine/terrigenous origin of CDOM in the EGC. Based on CDOM absorption in Polar Water and comparison with an Arctic river discharge weighted mean, we estimate that a 49-59% integrated loss of CDOM absorption across 250-600 nm has occurred. A preferential removal of absorption at longer wavelengths reflects the loss of high molecular weight material. In contrast, CDOM fluxes through the Fram Strait using September velocity fields from a high-resolution ocean-sea ice model indicate that the net southward transport of terrigenous CDOM through the Fram Strait equals up to 50% of the total riverine CDOM input; this suggests that the Fram Strait export is a major sink of CDOM. These contrasting results indicate that we have to constrain the (C)DOM budgets for the Arctic Ocean much better and examine uncertainties related to using tracers to assess conservative mixing in polar waters. Citation: Granskog, M. A., C. A. Stedmon, P. A. Dodd, R. M. W. Amon, A. K. Pavlov, L. de Steur, and E. Hansen (2012), Characteristics of colored dissolved organic matter (CDOM) in the Arctic outflow in the Fram Strait: Assessing the changes and fate of terrigenous CDOM in the Arctic Ocean, J. Geophys. Res., 117, C12021, doi:10.1029/2012JC008075

In-situ calibration and validation of CryoSat-2 observations over Arctic first year sea ice north of Svalbard

Large areas of the Arctic Ocean are covered with sea ice, the extent, thickness, concentration and properties of which change seasonally, interannually and on longer time scales. The Arctic Ocean is often difficult to access, making satellite remote sensing the only means to obtain information about the sea ice on a pan-Arctic scale. In order to improve the processing and interpretation of satellite data and imagery, in-situ calibration and validation are necessary. In spring 2011, measurements on first year sea ice north of Svalbard were performed during two scientific cruises with the ships KV “Svalbard” and RV “Lance” as a part of the CryoVEx 2011 project. During these cruises, detailed measurements of snow and ice thickness, freeboard, and snow density were performed on ice stations and from a helicopter. The data collected contributes to the calibration and validation of the SIRAL sensor data from the CryoSat-2 radar altimeter satellite, which measures the freeboard of sea ice for estimating its thickness. In snow pits, the stratigraphy of the snow pack was recorded. The collected data are currently being integrated with satellite data, airborne observations from helicopter that measured ice thickness using an electromagnetic induction sounder (EM-bird) and conducted aerial photography, and a Twin-Otter aircraft carrying the ESA Airborne Synthetic Aperture and Interferometric Radar Altimeter System (ASIRAS) system, the airborne radar altimeter designed to simulate the SIRAL radar on board the satellite, as well as a laser scanner. The first analysis of airborne and in- situ data indicates that the ASIRAS radar altimeter used in this experiment did not fully penetrate the snow layer on top of the sea ice. The regional sea ice characteristics for the research area are described using SAR products, obtained from the Envisat and Radarsat-2 satellites, in order to improve the interpretation and conclusions of the CryoSat-2 calibration and validation

Changes in the marine carbonate system of the western Arctic: patterns in a rescued data set

A recently recovered and compiled set of inorganic carbon data collected in the Canadian Arctic since the 1970s has revealed substantial change, as well as variability, in the carbonate system of the Beaufort Sea and Canada Basin. Whereas the role of this area as a net atmospheric carbon sink has been confirmed, high pCO2 values in the upper halocline underscore the potential for CO2 outgassing as sea ice retreats and upwelling increases. In addition, increasing total inorganic carbon and decreasing alkalinity are increasing pCO2 and decreasing CaCO3 saturation states, such that undersaturation with respect to aragonite now occurs regularly in both deep waters and the upper halocline