Molecular dissolved organic matter composition in lakes across Sweden as relative intensities of FT-ICR-MS peaks and PARAFAC components and optical indices

Whether intrinsic molecular properties or extrinsic factors such as environmental conditions control the decomposition of natural organic matter across soil, marine and freshwater systems has been subject to debate. Comprehensive evaluations of the controls that molecular structure exerts on organic matter's persistence in the environment have been precluded by organic matter's extreme complexity. Here we examine dissolved organic matter from 109 Swedish lakes using ultrahigh-resolution mass spectrometry and optical spectroscopy to investigate the constraints on its persistence in the environment. We find that degradation processes preferentially remove oxidized, aromatic compounds, whereas reduced, aliphatic and N-containing compounds are either resistant to degradation or tightly cycled and thus persist in aquatic systems. The patterns we observe for individual molecules are consistent with our measurements of emergent bulk characteristics of organic matter at wide geographic and temporal scales, as reflected by optical properties. We conclude that intrinsic molecular properties are an important control of overall organic matter reactivity.

Pb isotope and geochemical record of Arctic sediments

Elemental and Pb isotope measurements were performed on leachates and residues from surface sediments and two <50 cm cores (MC04 and MC16) collected along a NE-SW transect through Fram Strait. Geochemical and isotopic properties of residues from surface sediments define three distinct spatial domains within the Strait: 1) the easternmost edge of the Strait; 2) the eastern part of the Strait off the Svalbard margins; and 3) the western part of the Strait, influenced by supplies from Svalbard, the Nordic seas with possible contributions from northwestern Siberian margins, and sea ice and water outflow from the Arctic, respectively. Core MC16, in the third domain beneath the outflowing Arctic waters, spans the Last Glacial Maximum present interval. Sediments from this core were leached to obtain detrital (residues) and exchangeable (leachates) fractions. Detrital supplies to core MC16 are believed to originate mainly from melting of the overlying sea ice and thus can be used to document changes in Arctic sedimentary sources. Detrital 206Pb/204Pb and 208Pb/206Pb ratios illustrate two mixing trends, Trends A and B, corresponding to the pre- and post-Younger Dryas (YD) intervals, respectively. These trends represent binary mixtures with a common end-member (Canadian margins) and either a Siberian (Trend A) or Greenland (Trend B) margin end-member. The YD is marked by an isotopic excursion toward the Canadian end-member, suggesting a very active Beaufort Gyre possibly triggered by massive drainage of the Laurentide ice sheet. Pb isotope compositions of leachates, thought to represent the signature of the overlying water masses, define a unique linear trend coincident with Trend A. This suggests that water masses acquired their signature through exchange with particulate fluxes along the Canadian and Siberian continental margins.

Enzyme activities of digestive and metabolic enzymes of Calanus finmarchicus from Maria S. Merian cruise MSM26 in spring 2013

The present study aimed to contribute to the knowledge on the intraspecific variations of enzyme activities in populations of Calanus finmarchicus from different longitudes across the North Atlantic Ocean and their relation to changing environmental conditions. C. finmarchicus was sampled across the North Atlantic in basins with decreasing temperature regimes from east to west (Iceland Basin, Irminger Basin and Labrador Basin) in late March/early April 2013. Potential maximum enzyme activities of digestive (proteinases and lipases/esterases) and metabolic (citrate synthase) enzymes of copepods from all sampling stations were analysed and thermal profiles (5-50°C) of enzyme activities were determined. In order to investigate its acclimation potential, C. finmarchicus were acclimated to 4°C and 15°C for two weeks and thermal profiles of enzyme activities were compared afterwards.

Interactive effects of salinity and elevated CO2 levels on juvenile eastern oysters, Crassostrea virginica

Rising levels of atmospheric CO2 lead to acidification of the ocean and alter seawater carbonate chemistry, which can negatively impact calcifying organisms, including mollusks. In estuaries, exposure to elevated CO2 levels often co-occurs with other stressors, such as reduced salinity, which enhances the acidification trend, affects ion and acid-base regulation of estuarine calcifiers and modifies their response to ocean acidification. We studied the interactive effects of salinity and partial pressure of CO2 (PCO2) on biomineralization and energy homeostasis in juveniles of the eastern oyster, Crassostrea virginica, a common estuarine bivalve. Juveniles were exposed for 11 weeks to one of two environmentally relevant salinities (30 or 15 PSU) either at current atmospheric PCO2 (400 µatm, normocapnia) or PCO2 projected by moderate IPCC scenarios for the year 2100 (700-800 µatm, hypercapnia). Exposure of the juvenile oysters to elevated PCO2 and/or low salinity led to a significant increase in mortality, reduction of tissue energy stores (glycogen and lipid) and negative soft tissue growth, indicating energy deficiency. Interestingly, tissue ATP levels were not affected by exposure to changing salinity and PCO2, suggesting that juvenile oysters maintain their cellular energy status at the expense of lipid and glycogen stores. At the same time, no compensatory upregulation of carbonic anhydrase activity was found under the conditions of low salinity and high PCO2. Metabolic profiling using magnetic resonance spectroscopy revealed altered metabolite status following low salinity exposure; specifically, acetate levels were lower in hypercapnic than in normocapnic individuals at low salinity. Combined exposure to hypercapnia and low salinity negatively affected mechanical properties of shells of the juveniles, resulting in reduced hardness and fracture resistance. Thus, our data suggest that the combined effects of elevated PCO2 and fluctuating salinity may jeopardize the survival of eastern oysters because of weakening of their shells and increased energy consumption.