Mid-Wisconsin to Holocene permafrost and landscape dynamics based on a drained lake basin core from the northern Seward Peninsula, Northwest Alaska

Permafrost-related processes drive regional landscape dynamics in the Arctic terrestrial system. A better understanding of past periods indicative of permafrost degradation and aggradation is important for predicting the future response of Arctic landscapes to climate change. Here, we used a multi-proxy approach to analyze a ~4 m long sediment core from a drained thermokarst lake basin on the northern Seward Peninsula in western Arctic Alaska (USA). Sedimentological, biogeochemistical, geochronological, micropaleontological (ostracoda, testate amoeba) and tephra analyses were used to determine the long-term environmental Early-Wisconsin to Holocene history preserved in our core for Central Beringia. Yedoma accumulation dominated throughout the Early to Late-Wisconsin but was interrupted by wetland formation from 44.5 to 41.5 ka BP. The latter was terminated by deposition of 1 m of volcanic tephra, most likely originating from the South Killeak Maar eruption at about 42 ka BP. Yedoma deposition continued until 22.5 ka BP and was followed by a depositional hiatus in the sediment core between 22.5 and 0.23 ka BP. We interpret this hiatus as due to intense thermokarst activity in the areas surrounding the site, which served as a sediment source during the Late-Wisconsin to Holocene climate transition. The lake forming the modern basin on the upland initiated around 0.23 ka BP, which drained catastrophically in spring 2005. The present study emphasizes that Arctic lake systems and periglacial landscapes are highly dynamic and permafrost formation as well as degradation in Central Beringia was controlled by regional to global climate patterns and as well as by local disturbances.

Diatoms, total organic carbon, and total nitrogen of sediment core Dethlingen, Germany

To provide insights into the long-term evolution of aquatic ecosystems without human interference, we here evaluate a decadal- to centennial-scale-resolution diatom record spanning about 12 ka of the Holsteinian interglacial (Marine Isotope Stage 11c). Using a partially varved sediment core from the Dethlingen palaeolake (northern Germany), which has previously been studied for palynological and microfacies signals, we document the co-evolution of the aquatic and surrounding terrestrial environment. The diatom record is dominated by the genera Stephanodiscus, Aulacoseira, Ulnaria and Fragilaria. Based on the diatom assemblages and physical sediment properties, the evolution of the Dethlingen palaeolake can be subdivided into three major phases. During the oldest phase (lasting ~1900 varve years), the lake was ~10-15 m deep and characterized by anoxic bottom-water conditions and a high nutrient content. The following ~5600 years exhibited water depths >20 m, maximum diatom and Pediastrum productivity, and a peak in allochtonous nutrient input. During this phase, water-column mixing became more vigorous, resulting in a breakdown of anoxia. The youngest lake phase (~4000-5000 years) was characterized by decreasing water depth, turbulent water conditions and decreased nutrient loading. Based on our palaeolimnological data, we conclude that the evolution of the Dethlingen palaeolake during the Holsteinian interglacial responded closely to (i) changes within the catchment area (as documented by vegetation and sedimentation) related to the transition from closed forests growing on nutrient-rich soils (mesocratic forest phase) to open forests developing on poor soils (oligocratic forest phase), and (ii) short-term climate variability as reflected in centennial-scale climate perturbations.

Concentrations of organic carbon, nitrogen and phosphorus on vertical profiles in waters of the tropical North Atlantic in March 2002

In the literature, an inconsistency exists between estimates of biotically-effected carbon export inferred from large-scale geochemical studies (Jenkins 1982; 47 gC m-2 a-1) and local measurements of turbulent nutrient supply (Lewis et al. 1986; 4 gC m-2 a-1) in the eastern subtropical North Atlantic. Nutrient supply to the upper ocean by turbulent mixing is reexamined using local standard oceanographic measurements and high-resolution vertical profiles of nutrients averaged over a large region directly comparable to that investigated by Jenkins (1982). Turbulent fluxes induced by internal waves and salt fingering, respectively, are separated according to Gregg (1989) and Zhang et al. (1998). Nutrient transport into the nutrient-consuming surface layer by salt fingering is more than fivefold higher than transport due to internal-wave induced turbulence. Still, this cannot resolve the above- mentioned apparent inconsistency, even if additional physical transport mechanisms such as eddy pumping, advection and horizontal diffusion are accounted for. Estimated nitrate fluxes due to vertical turbulent diffusion are 0.05-0.15 mol m-2 a-1, corresponding to 4-11 gC m-2 a-1. Observed NO3/PO4 turbulent flux ratios of up to 23 are interpreted as the imprint of N2 fixation.

Concentrations of dissolved organic carbon and particulate organic nitrogen in the Eastern North Pacific

Data are presented on concentration of dissolved organic carbon and particulate organic nitrogen in sea water at four stations, and also of dissolved and particulate amino acids at a deep-sea station above the Japan Trench. Concentration of Corg ranged from 0.79 to 2.00 mg/l, reaching maximum in the upper productive layers, while that of particulate Norg varied from 0.0018 to 0.037 mg/l, the maximum being in the upper layer (0-100 m). Water and particulate matter contained 18 amino acids in concentrations varying from 0.150 to 0.177 mg/l in the former and from 0.010 to 0.048 mg/l in the latter. Amino acid composition is variable. Vertical distribution of dissolved Corg and particulate Norg, as well as of dissolved and particulate amino acids is greatly dependent on water dynamics.

Impact of CO2 enrichment on organic matter dynamics during nutrient induced coastal phytoplankton blooms

A mesocosm experiment was conducted to investigate the impact of rising fCO2 on the build-up and decline of organic matter during coastal phytoplankton blooms. Five mesocosms (~38 m³ each) were deployed in the Baltic Sea during spring (2009) and enriched with CO2 to yield a gradient of 355-862 µatm. Mesocosms were nutrient fertilized initially to induce phytoplankton bloom development. Changes in particulate and dissolved organic matter concentrations, including dissolved high-molecular weight (>1 kDa) combined carbohydrates, dissolved free and combined amino acids as well as transparent exopolymer particles (TEP), were monitored over 21 days together with bacterial abundance, and hydrolytic extracellular enzyme activities. Overall, organic matter followed well-known bloom dynamics in all CO2 treatments alike. At high fCO2, higher dPOC:dPON during bloom rise, and higher TEP concentrations during bloom peak, suggested preferential accumulation of carbon-rich components. TEP concentration at bloom peak was significantly related to subsequent sedimentation of particulate organic matter. Bacterial abundance increased during the bloom and was highest at high fCO2. We conclude that increasing fCO2 supports production and exudation of carbon-rich components, enhancing particle aggregation and settling, but also providing substrate and attachment sites for bacteria. More labile organic carbon and higher bacterial abundance can increase rates of oxygen consumption and may intensify the already high risk of oxygen depletion in coastal seas in the future.

Long-term dynamics of adaptive evolution in a globally important coccolithophore to ocean acidification

Recent evolution experiments have revealed that marine phytoplankton may adapt to global change, for example to ocean warming or acidification. Long-term adaptation to novel environments is a dynamic process and phenotypic change can take place thousands of generations after exposure to novel conditions. Using the longest evolution experiment performed in any marine species to date (4 yrs, = 2100 generations), we show that in the coccolithophore Emiliania huxleyi, long-term adaptation to ocean acidification is complex and initial phenotypic responses may revert for important traits. While fitness increased continuously, calcification was restored within the first 500 generations but later reduced in response to selection, enhancing physiological declines of calcification in response to ocean acidification. Interestingly, calcification was not constitutively reduced but revealed rates similar to control treatments when transferred back to present-day CO2 conditions. Growth rate increased with time in controls and adaptation treatments, although the effect size of adaptation assessed through reciprocal assay experiments varied. Several trait changes were associated with selection for higher cell division rates under laboratory conditions, such as reduced cell size and lower particulate organic carbon content per cell. Our results show that phytoplankton may evolve phenotypic plasticity that can affect biogeochemically important traits, such as calcification, in an unforeseen way under future ocean conditions.