Sand fraction, organic carbon and nitrogen data, and calculated marine and terrestrial organic carbon fractions of surface sediments in the western Barents Sea

There is generally a lack of knowledge on how marine organic carbon accumulation is linked to vertical export and primary productivity patterns. In this study, a multi-proxy geochemical and organic-sedimentological approach is coupled with organic facies modelling focusing on regional calculations of carbon cycling and carbon burial on the western Barents Shelf between northern Scandinavia and Svalbard. OF-Mod 3D, an organic facies modelling software tool, is used to reconstruct the marine and terrestrial organic carbon fractions and to make inferences about marine primary productivity in this region. The model is calibrated with an extensive sample dataset and reproduces the present-day regional distribution of the organic carbon fractions well. Based on this new organic facies model, we present regional carbon mass accumulation rate calculations for the western Barents Sea. The calibration dataset includes location and water depth, sand fraction, organic carbon and nitrogen data and calculated marine and terrestrial organic carbon fractions.

Geochemistry of surface sediment samples from the western Barents Sea region

Here, we present bulk organic geochemical data from a spatial grid of surface samples from the western Barents Sea region. The results show that the distribution of organic carbon in surface sediments is predominantly controlled by input from land-derived terrigenous and in-situ produced marine organic matter. Inferred from various nitrogenous fractions and stable isotopes of bulk organic carbon we show that the spatial distribution of terrigenous organic carbon is independent of water depth, organic carbon mineralization and variable sedimentation rates. Instead, the pattern is predominantly controlled by sea ice-induced lateral transport and subsequent release in the Marginal Ice Zone (MIZ) as well as the distance to shore. Consistent with the observation of high vertical flux of particulate organic material in the MIZ, are amounts of marine organic carbon significantly enhanced in sediments below the winter ice margin. This is in accordance with modern observations suggesting that Arctic shelves with seasonal ice zones can be hot spots of vertical carbon export and thus a potential CO2 sink.

Chemistry of interstitial water of samples from DSDP Leg 38

Interstitial waters recovered during Leg 38 show large changes in major ion composition and also in oxygen isotope composition. Increases in Ca[++] and Sr[++] and decreases in K[+], Mg[++], and O18/O16 are interpreted in terms of extensive diagenesis of terrigenous, volcanic, or basaltic igneous materials in the sediments and underlying basalts. Slight, but well-established increases in chlorinity with depth indicate that these postulated weathering reactions involve uptake of water to a measurable extent. Interstitial waters from sites drilled on the Inner Voring Plateau suggest the infusion of fresh waters by aquifers from the mainland of Norway.

Sea surface temperatures and UK37 of three sediment cores from the Arctic Ocean

Sediment proxy data from the Norwegian, Greenland, and Iceland seas (Nordic seas) are presented to evaluate surface water temperature (SST) differences between Holocene and Eemian times and to deduce from these data the particular mode of surface water circulation. Records from planktic foraminiferal assemblages, CaCO3 content, oxygen isotopes of foraminifera, and iceberg-rafted debris form the main basis of interpretation. All results indicate for the Eemian comparatively cooler northern Nordic seas than for the Holocene due to a reduction in the northwardly flow of Atlantic surface water towards Fram Strait and the Arctic Ocean. Therefore, the cold polar water flow from the Arctic Ocean was less influencial in the southwestern Nordic seas during this time. As can be further deduced from the Eemian data, slightly higher Eemian SSTs are interpreted for the western Iceland Sea compared to the Norwegian Sea (ca. south of 70°N). This Eemian situation is in contrast to the Holocene when the main mass of warmest Atlantic surface water flows along the Norwegian continental margin northwards and into the Arctic Ocean. Thus, a moderate northwardly decrease in SST is observed in the eastern Nordic seas for this time, causing a meridional transfer in ocean heat. Due to this distribution in SSTs the Holocene is dominated by a meridional circulation pattern. The interpretation of the Eemian data imply a dominantly zonal surface water circulation with a steep meridional gradient in SSTs.

Global compilation of benthic data sets I

Approaches to quantify the organic carbon accumulation on a global scale generally do not consider the small-scale variability of sedimentary and oceanographic boundary conditions along continental margins. In this study, we present a new approach to regionalize the total organic carbon (TOC) content in surface sediments (<5 cm sediment depth). It is based on a compilation of more than 5500 single measurements from various sources. Global TOC distribution was determined by the application of a combined qualitative and quantitative-geostatistical method. Overall, 33 benthic TOC-based provinces were defined and used to process the global distribution pattern of the TOC content in surface sediments in a 1°x1° grid resolution. Regional dependencies of data points within each single province are expressed by modeled semi-variograms. Measured and estimated TOC values show good correlation, emphasizing the reasonable applicability of the method. The accumulation of organic carbon in marine surface sediments is a key parameter in the control of mineralization processes and the material exchange between the sediment and the ocean water. Our approach will help to improve global budgets of nutrient and carbon cycles.

Compilation of 220 sediment core d13C data from the glacial Atlantic Ocean

We compare a compilation of 220 sediment core d13C data from the glacial Atlantic Ocean with three-dimensional ocean circulation simulations including a marine carbon cycle model. The carbon cycle model employs circulation fields which were derived from previous climate simulations. All sediment data have been thoroughly quality controlled, focusing on epibenthic foraminiferal species (such as Cibicidoides wuellerstorfi or Planulina ariminensis) to improve the comparability of model and sediment core carbon isotopes. The model captures the general d13C pattern indicated by present-day water column data and Late Holocene sediment cores but underestimates intermediate and deep water values in the South Atlantic. The best agreement with glacial reconstructions is obtained for a model scenario with an altered freshwater balance in the Southern Ocean that mimics enhanced northward sea ice export and melting away from the zone of sea ice production. This results in a shoaled and weakened North Atlantic Deep Water flow and intensified Antarctic Bottom Water export, hence confirming previous reconstructions from paleoproxy records. Moreover, the modeled abyssal ocean is very cold and very saline, which is in line with other proxy data evidence.

Morphology of Cycladophora davisiana davisiana from the Atlantic Ocean

In recent years, temporal fluctuations in the abundance of C. d. davisiana have been used frequently as a highresolution stratigraphic and paleoenvironmental tool. The modern ecology and morphologic variation (temporal and geographic) of this radiolarian species is evaluated to ascertain its potential stratigraphic and paleoenvironmental significance. Statistics were obtained on the width and height of all C. d. davisiana segments from Pleistocene populations of differing ages from the Northern Hemisphere (Labrador Sea and Iceland-Faeroe Ridge) and Southern Hemisphere (Namibian shelf and Meteor Rise). Results reveal that segment height variations between and within populations are more conservative than segment width. The mean sizes of the thorax and first abdominal segment have distinguishable differences between C. d. davisiana found in the North and South Atlantic. All populations have no significant difference in first abdominal segment width, however, mean heights of this segment differ greatly between populations of the North and South Atlantic. Second abdominal segment sizes show no clear population grouping. Size differences in post-cephalic segment size of these populations would appear to be related to some isolation of gene pools and possibly unknown paleoenvironmental factors. Temporal changes in the postcephalic size of C. d. davisiana may be used to: (1) identify temporally equivalent peaks in abundance of the species in a given region, (2) possibly evaluate the degree of mixing of water'masses between regions, and (3) trace the initial spread of the species from its area of origin. Cleve's 1887 plankton samples, between Greenland and Spitzsbergen, were studied and used in conjunction with other data to make the following conclusions on the modern ecology of C. d. davisiana in the Arctic and Greenland-Norwegian Seas. (1) It is presently absent in surface water plankton samples, (2) it currently lives at depths below 500 m, where it is rare, (3) it does not live in the upper 200 m under Arctic ice but is rare at greater depths, (4) it is absent in the upper 200 m near permanent Greenland Sea ice where normal oceanic salinity prevails, and (5) it is most common in deep marginal fjord environments which may serve as a refuge for the species during interglacial periods. In the Atlantic Ocean, the abundance of C. d. davisiana does not exceed 1% of the assemblage between the Subtropical Convergence of each hemisphere. In the Norwegian and Labrador Seas the species may occasionally be in the range of 1-5% of the modern radiolarian assemblage and never more than 5% in the southern high latitudes. Apparently only in the modern Sea of Okhotsk, does the species presently occur in high abundance. We concur with Morley and Hays (1983) that increased abundances are likely caused by the development of a strong low-salinity surface layer associated with seasonal sea ice melting and a strong temperature minimum above warmer and higher salinity intermediate waters. Similar conditions were frequent during the Pleistocene in the high latitudes and its modern scarcity outside the Sea of Okhotsk must be related to the absence of the presently unique conditions in the latter region.

(Table 2) Abundance of Radiolaria species in sediment samples from Core AMK4-340

Over the past 13 kyr the most significant natural changes in the Reykjanes ridge region took place within 13-7.8 kyr B.P. They resulted from alternating intensifications of the influence of the Labrador (LWM) and Norwegian-Greenland (NGWM) water masses. During 13-11.7 kyr B.P. natural conditions were governed by influence of LWM with sea surface temperature (SST) 3-5°C lower present one. During 11.7-10.3 kyr B.P. NGWM with SST 6-7°C lower present one predominated. During 10.3-9.5 kyr B.P. oceanographic conditions were rapidly transforming and approaching present ones controlled by interaction between LWM and North Atlantic water masses; SST abruptly increased almost to the present value. During 9.5-8.3 kyr B.P. intensification of NGWM led to small decrease of SST (1.5-2.5°C below present value; between 8.3 and 7.8 kyr B.P. natural conditions had approximated present ones and later on remained relatively stable; SST fluctuated with an amplitude of about 1.5°C.

Abundance, biomass and secondary production of benthic megafauna on the Barents Sea shelf in 2008 and 2009

Megabenthos plays a major role in the overall energy flow on Arctic shelves, but information on megabenthic secondary production on large spatial scales is scarce. Here, we estimated for the first time megabenthic secondary production for the entire Barents Sea shelf by applying a species-based empirical model to an extensive dataset from the joint Norwegian? Russian ecosystem survey. Spatial patterns and relationships were analyzed within a GIS. The environmental drivers behind the observed production pattern were identified by applying an ordinary least squares regression model. Geographically weighted regression (GWR) was used to examine the varying relationship of secondary production and the environment on a shelfwide scale. Significantly higher megabenthic secondary production was found in the northeastern, seasonally ice-covered regions of the Barents Sea than in the permanently ice-free southwest. The environmental parameters that significantly relate to the observed pattern are bottom temperature and salinity, sea ice cover, new primary production, trawling pressure, and bottom current speed. The GWR proved to be a versatile tool for analyzing the regionally varying relationships of benthic secondary production and its environmental drivers (R² = 0.73). The observed pattern indicates tight pelagic? benthic coupling in the realm of the productive marginal ice zone. Ongoing decrease of winter sea ice extent and the associated poleward movement of the seasonal ice edge point towards a distinct decline of benthic secondary production in the northeastern Barents Sea in the future.

Physical oceanography from the TRACTOR project

Primary Objectives - Describe and quantify the present strength and variability of the circulation and oceanic processes of the Nordic Seas regions using primarily observations of the long term spread of a tracer purposefully released into the Greenland Sea Gyre in 1996. - Improve our understanding of ocean processes critical to the thermaholine circulation in the Nordic Seas regions so as to be able to predict how this region may respond to climate change. - Assess the role of mixing and ageing of water masses on the carbon transport and the role of the thermohaline circulation in carbon storage using water transports and mixing coefficients derived from the tracer distribution. Specific Objectives Perform annual hydrographic, chemical and SF6 tracer surveys into the Nordic regions in order to: - Measure lateral and diapycnal mixing rates in the Greenland Sea Gyre and in the surrounding regions. - Document the depth and rates of convective mixing in the Greenland Sea using the SF6 and the water masses characteristics. - Measure the transit time and transport of water from the Greenland Sea to surrounding seas and outflows. Document processes of water mass transformation and entrainment occurring to water emanating from the central Greenland Sea. - Measure diapycnal mixing rates in the bottom and margins of the Greenland Sea basin using the SF6 signal observed there. Quantify the potential role of bottom boundary-layer mixing in the ventilation of the Greenland Sea Deep Water in absence of deep convection. Monitor the variability of the entrainment of water from the Greenland Sea using time series auto-sampler moorings at strategic positions i.e., sill of the Denmark Strait, Labrador Sea, Jan Mayen fracture zone and Fram Strait. Relate the observed variability of the tracer signal in the outflows to convection events in the Greenland Sea and local wind stress events. Obtain a better description of deepwater overflow and entrainment processes in the Denmark Strait and Faeroe Bank Channel overflows and use these to improve modelling of deepwater overflows. Monitor the tracer invasion into the North Atlantic using opportunistic SF6 measurements from other cruises: we anticipate that a number of oceanographic cruises will take place in the north-east Atlantic and the Labrador Sea. It should be possible to get samples from some cruises for SF6 measurements. Use process models to describe the spread of the tracer to achieve better parameterisation for three-dimensional models. One reason that these are so resistant to prediction is that our best ocean models are as yet some distance from being good enough, to predict climate and climate change.