Photosynthetic production in the Central Arctic during POLARSTERN cruise ARK-XXVII/3 (IceArc) in 2012

The ice-covered Central Arctic Ocean is characterized by low primary productivity due to light and nutrient limitations. It has been speculated that the recent reduction in ice cover could lead to a substantial increase in primary production, but still little is known as to the fate of the ice-associated primary production, and of nutrient supply with increasing warming. This study presents results from the Central Arctic Ocean collected during summer 2012, when sea-ice reached a minimum extent since the onset of satellite observations. Net primary productivity (NPP) was measured in water column, sea ice and melt ponds by 14CO2 uptake at different irradiances. Photosynthesis vs. irradiance (PI) curves were established in laboratory experiments and used to upscale measured NPP to the deep Eurasian Basin (north of 78°N) using the irradiance-based Central Arctic Ocean Primary Productivity model (CAOPP). In addition, new annual production was calculated from the seasonal nutrient drawdown in the mixed layer since last winter. Results show that ice algae can contribute up to 60% to primary production in the Central Arctic at the end of the season. The ice-covered water column had lower NPP rates than open water probably due to light limitation. According to the nutrient ratios in the euphotic zone, nitrate limitation was detected in the Siberian Seas (Laptev Sea area), while silicate was the main limiting nutrient at the ice margin influenced by Atlantic waters. Although sea-ice cover was substantially reduced in 2012, total annual new production in the Eurasian Basin was 17 ± 7 Tg C/yr, which is similar to previous estimates. However, when including the contribution by sub-ice algal filaments, the annual production for the deep Eurasian Basin (north of 78°N) is 16 Tg C/yr higher than estimated before. Our data suggest that sub-ice algae might be responsible for potential local increases in NPP due to higher light availability under the ice, and their ability to benefit from a wider area of nutrients as they drift with the ice.

Compilation of measurements from two interdisciplinary STAR-shaped surveys in the North Sea: The ZISCH - Dataset

The measurements were obtained during two North Sea wide STAR-shaped cruises during summer 1986 and winter 1987, which were performed to investigate the circulation induced transport and biologically induced pollutant transfer within the interdisciplinary research in the project "ZISCH - Zirkulation und Schadstoffumsatz in der Nordsee / Circulation and Contaminant Fluxes in the North Sea (1984-1989)". The inventory presents parameters measured on hydrodynamics, nutrient dynamics, ecosystem dynamics and pollutant dynamics in the pelagic and benthic realm. The research program had the objective of quantifying fluxes of major budgets, especially contaminants in the North Sea. In spring 1986, following the phytoplankton spring bloom, and in late winter 1987, at minimum primary production activity, the North Sea ecosystem was investigated on a station net covering the whole North Sea. The station net was shaped like a star. Sampling started in the centre, followed by the northwest section and moving counter clockwise around the North Sea following the residual currents. By this strategy, a time series was measured in the central North Sea and more synoptic data sets were obtained in the individual sections. Generally advection processes have to be considered when comparing the data from different stations. The entire sampling period lasted for more than six weeks in each cruise. Thus, a time-lag should be considered especially when comparing the data from the eastern and the western part of the central and northern North Sea, where samples were taken at the beginning and at the end of the campaign. The ZISCH investigations represented a qualitatively and quantitatively new approach to North Sea research in several respects. (1) The first simultaneous blanket coverage of all important biological, chemical and physical parameters in the entire North Sea ecosystem; (2) the first simultaneous measurements of major contaminants (metals and organohaline compounds) in the different ecosystem compartments; (3) simultaneous determinations of atmospheric inputs of momentum, energy and matter as important ecosystem boundary conditions; (4) performance of the complex measurement program during two seasons, namely the spring plankton bloom and the subsequent winter period of minimal biological activity; and (5) support of data analysis and interpretation by oceanographic and meteorological numerical models on the same scales.

Geochemistry of lavas and dikes from the upper oceanic crust of Hess Deep Rift, eastern Pacific Ocean

Strontium isotopes are useful tracers of fluid-rock interaction in marine hydrothermal systems and provide a potential way to quantify the amount of seawater that passes through these systems. We have determined the whole-rock Sr-isotopic compositions of a section of upper oceanic crust that formed at the fast-spreading East Pacific Rise, now exposed at Hess Deep. This dataset provides the first detailed comparison for the much-studied Ocean Drilling Program (ODP) drill core from Site 504B. Whole-rock and mineral Sr concentrations indicate that Sr-exchange between hydrothermal fluids and the oceanic crust is complex, being dependent on the mineralogical reactions occurring; in particular, epidote formation takes up Sr from the fluid increasing the 87Sr/86Sr of the bulk-rock. Calculating the fluid-flux required to shift the Sr-isotopic composition of the Hess Deep sheeted-dike complex, using the approach of Bickle and Teagle (1992, doi:10.1016/0012-821X(92)90221-G) gives a fluid-flux similar to that determined for ODP Hole 504B. This suggests that the level of isotopic exchange observed in these two regions is probably typical for modern oceanic crust. Unfortunately, uncertainties in the modeling approach do not allow us to determine a fluid-flux that is directly comparable to fluxes calculated by other methods.

Mineralogy and inorganic geochemistry of sediments at DSDP Leg 65 Holes

During Leg 65, 15 holes were drilled at four sites located on young crust in the mouth of the Gulf of California. Quaternary to upper Pliocene hemipelagic sediments above and interlayered within the young basaltic basement were cored. The influence of hot lava, high temperature gradients, and hydrothermal activity on the mineralogy and geochemistry of the terrigenous sediments near contacts with basalts might therefore be expected. The purpose of the present study was to determine the mineralogy and inorganic geochemistry of these sediments and to analyze the nature and extent of low temperature alteration. To this end we studied the mineralogy and inorganic geochemistry of 75 sediment samples, including those immediately overlying uppermost basalts and those from layers alternating with basalts within the basement. We separated three size fractions - <2 µm (clay), 2-20 µm (intermediate), and >20 µm (coarse) - and applied the following mineralogical determinations: x-ray diffraction (XRD), infrared spectroscopy, transmission and scanning electron microscopy, and optical microscopy (for coarse fractions, using thin sections and smear slides). We calculated the percentages of clay minerals using Biscaye's (1964) method, and used routine wet chemical analyses to determine bulk composition and quantitative spectral analyses for trace elements.

Holocene sediment transport from the glaciated margin of East/Northeast Greenland to the N Iceland shelves

We examine variations in the ice-rafted sources for sediments in the Iceland/East Greenland offshore marine archives by utilizing a sediment unmixing model and link the results to a coupled iceberg-ocean model. Surface samples from around Iceland and along the E/NE Greenland shelf are used to define potential sediment sources, and these are examined within the context of the down-core variations in mineralogy in the <2 mm sediment fraction from a transect of cores across Denmark Strait. A sediment unmixing model is used to estimate the fraction of sediment <2 mm off NW and N Iceland exported across Denmark Strait; this averaged between 10 and 20%. Both the sediment unmixing model and the coupled iceberg-ocean model are consistent in finding that the fraction of "far-travelled" sediments in the Denmark Strait environs is overwhelmingly of local, mid-East Greenland, provenance, and therefore with a significant cross-channel component to their travel. The Holocene record of ice-rafted sediments denotes a three-part division of the Holocene in terms of iceberg sediment transport with a notable increase in the process starting ca 4000 cal yr BP. This latter increase may represent the re-advance during the Neoglacial period of land-terminating glaciers on the Geikie Plateau to become marine-terminating. The contrast in spectral signals between these cores and the 1500-yr cycle at VM28-14, just south of the Denmark Strait, combined with the coupled iceberg-model results, leads us to speculate that the signal at VM28-14 reflects pulses in overflow waters, rather than an ice-rafted signal.

Mesozooplankton investigations in Bornholm Basin, Baltic Sea

Mesozooplankton production was estimated by using a new sampling technique and two alternative calculation methods. In essence, production estimates are based on significantly higher abundances. The contribution of juvenile stages to copepod and fish dynamics was generally low, so that the omission of juvenile stages in budgets will result in a small error. The situations reported in this study present a unique food web szenario, which in detail, however, was strongly dependent on methodology. Furthermore relations between trophic levels were considered with respect to vertical distribution.

Mineral and chemical compositions of sedimentary and volcano-sedimentary rocks drilled in DSDP Legs 43 and 44

Sedimentary cover on the bottom of the Northwest Atlantic Ocean is underlain by Late Jurassic - Cretaceous tholeiite-basalt formation. It consists of come sedimentary formations with different lithologic features and age. Their composition, stratigraphic position and, distribution are described on materials of deep-sea drilling. Mineralogical and geochemical studies of DSDP Leg 43 and Leg 44 holes lead to new ideas about composition and genesis of some sediment types of and their associations. High metal contents in the chalk formation of black clays on the Bermuda Rise probably result from exhalations. Connection of red-colored and speckled deposits with hiatuses in sedimentation is shown. Main stages of geological history of the North American Basin are reflected in accumulation of the followed formations: ancient carbonate formation (Late Jurassic - Early Cretaceous), formation of black clays rich in organic matter (Cretaceous), formation of speckled clays (Late Cretaceous), siliceous-clayey turbidite formation (Eocene), hemipelagic and pelagic clayey formation (Neogene), and terrigenous turbidite formation (Pleistocene).

Physical properties, mineral and chemical compositions, and accumulation rates of Holocene and Upper Pleistocene bottom sediments from the Sea of Okhotsk

Mineral and chemical compositions and physical properties of diatomaceous clayey-siliceous sediments from the Sea of Okhotsk are studied. Accumulation rates of silica are determined. Their compositional model based on silica content is similar to that of Late Jurassic and Olenekian-Middle Anisian cherts from the Sikhote Alin region. Thickness of Holocene siliceous unit and accumulation rates of siliceous deposits depended on bioproductivity in the upper water layer and seafloor topography. Accumulation rates of amorphous SiO2 (0.05-5.7 g/cm**2/ka) and free SiO2 (0.5-11.6 g/cm**2/ka) are minimal on seamounts and maximal in depressions near foothills. These values match accumulation rates of free SiO2 in Triassic and Late Jurassic basins of the Sikhote Alin region (0.33-3 g/cm**2/ka). Comparison of composition and accumulation rates of silica shows that Triassic and Late Jurassic siliceous sequences of Sikhote Alin could accumulate in a marginal marine basin near a continent.

Clay mineralogy of ODP Site 188-1165

The Ocean Drilling Program Leg 188 Site 1165 was drilled on the Wild Drift on the Continental Rise off Prydz Bay, East Antarctica to a total depth of 999.1 meters below seafloor (mbsf). It recovered an extensive suite of terrigenous and hemipelagic sediments of early Miocene to Pleistocene age. Of special interest in this study is the sediment column between 0 and 50 mbsf, which consists of a well-preserved section of Pliocene-Pleistocene-age sediments that was sampled at 10-cm intervals. Multiproxy study of this interval could show possible intervals of expansions of the ice-sheet across the continental shelves and express the climatic evolution in Antarctica, particularly during the 'middle' Pliocene warm period (3.15 to 2.85 Ma) which may provide an indication of how the Earth responds to a rise of its surface temperature. According to the existing age model, the upper 50 mbsf stratigraphic sequence of Site 1165 reaches back to ~4.9 Ma. Throughout this interval, the clay-mineral content is characterized by fluctuations of individual clay minerals, particularly smectite and chlorite. The smectite concentration varies mainly between 0% and 30%. Illite fluctuates less between 50% and 80%, and kaolinite varies mainly between 10% and 20%. Chlorite concentrations are mainly 0% to 10%. There is also a noticeable change in magnetic susceptibility at ~34 mbsf that is clearly indicated in the composition of the clay-mineral suite. At this level, smectite decreases and illite, kaolinite and chlorite show some variability. In particular, there is a slight but persistent increase in chlorite. The results from the Plio-Pleistocene transition, with evenly fluctuating smectite and illite contents and the gradually increasing chlorite content, may indicate cooler conditions compared to the mid-Pliocene conditions. Slight increase in illite content and decrease in smectite content towards Pleistocene supports the previous assumption. The results from the mid-Pliocene with the increasing smectite content and decreasing illite content may indicate warmer and possibly interglacial conditions.

Biological traits, and egg and fecal pellet production of Calanus finmarchicus and Calanus glacialis in situ and during experiments

The effects of temperature and food was examined for Calanus finmarchicus and C. glacialis during 3 phases of the phytoplankton spring bloom in Disko Bay, western Greenland. The 2 species were collected during pre-bloom, bloom, and post-bloom and exposed to temperatures from 0 to 10°C, combined with deficient or excess food. Fecal pellet and egg production were measured as indices for grazing and secondary production, respectively. Furthermore, changes in body carbon, nitrogen, and lipid content were measured. C. glacialis sampled before the bloom and incubated with excess food exhibited high specific egg production at temperatures between 0 and 2.5°C. Higher temperatures did not increase egg production considerably, whereas egg production for C. finmarchicus more than tripled between 2.5 and 5°C. Starved C. glacialis produced eggs at all temperatures stimulated by increasing temperatures, whereas starved C. finmarchicus needed temperatures above 5°C to produce eggs fueled by their lipid stores. Few C. finmarchicus had mature gonads at the initiation of the pre-bloom and bloom experiment, and egg production of C. finmarchicus therefore only increased as the ratio of individuals with mature gonads increased. During the bloom, both C. glacialis and C. finmarchicus used the high food availability for egg production, while refueling or exhausting their lipid stores, respectively. Finally, during the post-bloom experiment, production was low by C. finmarchicus, whereas C. glacialis had terminated production. Our results suggest that a future warmer ocean will reduce the advantage of early spawning by C. glacialis and that C. finmarchicus will become increasingly prevalent.

Data collection of depth and time integrated Calanus finmarchicus abundances, averaged temperatures, and integrated Chlorophyll concentration in the North Atlantic Ocean

Here we present a new, pan-North-Atlantic compilation of data on key mesozooplankton species, including the most important copepod, Calanus finmarchicus. Distributional data of eight representative zooplankton taxa, from recent (2000-2009) Continuous Plankton Recorder data, are presented, along with basin-scale data of the phytoplankton colour index. Then we present a compilation of data on C. finmarchicus, including observations of abundance, demography, egg production and female size, with accompanying data on temperature and chlorophyll. . This is a contribution by Canadian, European and US scientists and their institutions.

Pelagic, turbiditic, and contouritic sequential deposits on the Cape Verde Plateau

On the Cape Verde Plateau, Neogene deposits are composed of major pelagic and hemipelagic sediments. These sediments show climatic sequences composed of two lithologic terms that differ in their siliciclastic and carbonate contents. Several turbiditic and contouritic sequences are interbedded in these deposits. Turbidite sequences are fine grained and thin bedded with a very low frequency (about 12 sequences during the Neogene). They are composed of quartz-rich siliciclastic or volcaniclastic sediments. Quartz-rich turbidites originated from the Senegalese margin. Their slightly higher frequency during the early Pliocene indicates that the stronger turbidity currents, and probably the most abundant continental inputs, occur at that period. Volcaniclastic turbidites are only present in the early Miocene (about 17 Ma) and the early Pleistocene (1 Ma). They have flown from adjacent Cape Verde Islands and reflect two episodes of high volcanic activity in this area. Contourite sequences, composed of biogenic sandy silts, represent less than 5% of the sediment pile and seem to have been mainly deposited during the late Pleistocene. These different sequences show clay mineral variations throughout Neogene time. Kaolinite is predominant in the Miocene and lower Pliocene deposits; this mineral decreases thereafter, with an increased trend of illite in the uppermost Pliocene and Pleistocene sediments, suggesting a change in sediment sources on the Saharan continent at about 2.6 Ma.

Sedimentary facies and clay mineralogy of ODP Site 105-646

The grain-size study and analyses of bulk sediment and clay mineral composition of samples collected from the dominant lithologies recovered at ODP Site 646, located on the northern flank of the Eirik Ridge (Labrador Sea), show variations indicating that contour-following currents, linked to Norwegian Sea Overflow Water (NSOW), have controlled sedimentation since the early Pliocene. These currents were influential until the early Pleistocene, despite the onset of major ice-rafting at about 2.5 Ma. A major mineralogical change occurred during the late Miocene: a decrease in the smectite to illite and chlorite ratio and a decrease of the crystallinity of smectites. This change indicates a renewing of the source rocks, which could result from an important hydrological change at this time. This change also is depicted by grain-size data that suggest the bottom current influence should be set earlier than the Pliocene.

Seasonal changes in labile organic matter composition on the continental shelf and bathyal sediments of the Cretan Sea

Bacterial abundance, biomass and cell size were studied in the oligotrophic sediments of the Cretan Sea (Eastern Mediterranean), in order to investigate their response to the seasonal varying organic matter (OM) inputs. Sediment samples were collected on a seasonal basis along a transect of seven stations (ranging from 40 to 1570 m depth) using a multiple-corer. Bacterial parameters were related to changes in chloroplastic pigment equivalents (CPE), the biochemical composition (proteins, lipids, carbohydrates) of the sedimentary organic matter and the OM flux measured at a fixed station over the deep basin (1570 m depth). The sediments of the Cretan Sea represent a nutrient depleted ecosystem characterised by a poor quality organic matter. All sedimentary organic compounds were found to vary seasonally, and changes were more evident on the continental shelf than in deeper sediments. Bacterial abundance and biomass in the sediments of the Cretan Sea (ranging from 1.02 to 4.59 * 10**8 cells/g equivalent to 8.7 and 38.7 µgC/g) were quite high and their distribution appeared to be closely related to the input of fresh organic material. Bacterial abundance and biomass were sensitive to changes in nutrient availability, which also controls the average cell size and the frequency of dividing cells. Bacterial abundance increased up to 3-fold between August '94 and February '95 in response to the increased amount of sedimentary proteins and CPE, indicating that benthic bacteria were constrained more by changes in quality rather than the quantity of the sedimentary organic material. Bacterial responses to the food inputs were clearly detectable down to 10 cm depth. The distribution of labile organic compounds in the sediments appeared to influence the vertical patterns of bacterial abundance and biomass. Cell size decreased significantly with water depth. Bacterial abundance and biomass were characterised by clear seasonal changes in response to seasonal OM pulses. The strong coupling between protein flux and bacterial biomass together with the strong bacterial dominance over the total biomass suggest that the major part of the carbon flow was channelled through the bacteria and the benthic microbial loop.