The influence of ocean acidification on nitrogen regeneration and nitrous oxide production in the northwest European shelf sea

The assimilation and regeneration of dissolved inorganic nitrogen, and the concentration of N2O, was investigated at stations located in the NW European shelf sea during June/July 2011. These observational measurements within the photic zone demonstrated the simultaneous regeneration and assimilation of NH4+, NO2- and NO3-. NH4+ was assimilated at 1.82-49.12 nmol N/L/h and regenerated at 3.46-14.60 nmol N/L/h; NO2- was assimilated at 0-2.08 nmol N/L/h and regenerated at 0.01-1.85 nmol N/L/h; NO3-was assimilated at 0.67-18.75 nmol N/L/h and regenerated at 0.05-28.97 nmol N/L/h. Observations implied that these processes were closely coupled at the regional scale and that nitrogen recycling played an important role in sustaining phytoplankton growth during the summer. The [N2O], measured in water column profiles, was 10.13 ± 1.11 nmol/L and did not strongly diverge from atmospheric equilibrium indicating that sampled marine regions were neither a strong source nor sink of N2O to the atmosphere. Multivariate analysis of data describing water column biogeochemistry and its links to N-cycling activity failed to explain the observed variance in rates of N-regeneration and N-assimilation, possibly due to the limited number of process rate observations. In the surface waters of five further stations, ocean acidification (OA) bioassay experiments were conducted to investigate the response of NH4+ oxidising and regenerating organisms to simulated OA conditions, including the implications for [N2O]. Multivariate analysis was undertaken which considered the complete bioassay data set of measured variables describing changes in N-regeneration rate, [N2O] and the biogeochemical composition of seawater. While anticipating biogeochemical differences between locations, we aimed to test the hypothesis that the underlying mechanism through which pelagic N-regeneration responded to simulated OA conditions was independent of location. Our objective was to develop a mechanistic understanding of how NH4+ regeneration, NH4+ oxidation and N2O production responded to OA. Results indicated that N-regeneration process responses to OA treatments were location specific; no mechanistic understanding of how N-regeneration processes respond to OA in the surface ocean of the NW European shelf sea could be developed.

CO2 and vitamin B12 interactions determine bioactive trace metal requirements of a subarctic Pacific diatom

Phytoplankton growth can be limited by numerous inorganic nutrients and organic growth factors. Using the subarctic diatom Attheya sp. in culture studies, we examined how the availability of vitamin B(12) and carbon dioxide partial pressure (pCO(2)) influences growth rate, primary productivity, cellular iron (Fe), cobalt (Co), zinc (Zn) and cadmium (Cd) quotas, and the net use efficiencies (NUEs) of these bioactive trace metals (mol C fixed per mol cellular trace metal per day). Under B(12)-replete conditions, cells grown at high pCO(2) had lower Fe, Zn and Cd quotas, and used those trace metals more efficiently in comparison with cells grown at low pCO(2). At high pCO(2), B(12)-limited cells had ~50% lower specific growth and carbon fixation rates, and used Fe ~15-fold less efficiently, and Zn and Cd ~3-fold less efficiently, in comparison with B(12)-replete cells. The observed higher Fe, Zn and Cd NUE under high pCO(2)/B(12)-replete conditions are consistent with predicted downregulation of carbon-concentrating mechanisms. Co quotas of B(12)-replete cells were 5- to 14-fold higher in comparison with B(12)-limited cells, suggesting that >80% of cellular Co of B(12)-limited cells was likely from B(12). Our results demonstrate that CO(2) and vitamin B(12) interactively influence growth, carbon fixation, trace metal requirements and trace metal NUE of this diatom. This suggests the need to consider complex feedback interactions between multiple environmental factors for this biogeochemically critical group of phytoplankton in the last glacial maximum as well as the current and future changing ocean.

Reason and Being of Engineering Geology

This paper demonstrates the importance of a holistic comprehension of the Earth like a planet that is alive, not only in its Biosphere, looking at the atmosphere-ocean-crust-mantle interactions as its different sectorial expressions (climate, fluid-dynamics, morpho-dynamics, tectonics…) following the solar radiation and nuclear geothermal sources of energy. It considers the environmental incidence of different engineering activities to realize their underfeeding as the raison, and leads to that holistic formation as the being of the engineering geology

Variability of the ocean heat content during the last millennium - an assessment with the ECHO-g Model

Studies addressing climate variability during the last millennium generally focus on variables with a direct influence on climate variability, like the fast thermal response to varying radiative forcing, or the large-scale changes in atmospheric dynamics (e. g. North Atlantic Oscillation). The ocean responds to these variations by slowly integrating in depth the upper heat flux changes, thus producing a delayed influence on ocean heat content (OHC) that can later impact low frequency SST (sea surface temperature) variability through reemergence processes. In this study, both the externally and internally driven variations of the OHC during the last millennium are investigated using a set of fully coupled simulations with the ECHO-G (coupled climate model ECHAMA4 and ocean model HOPE-G) atmosphere-ocean general circulation model (AOGCM). When compared to observations for the last 55 yr, the model tends to overestimate the global trends and underestimate the decadal OHC variability. Extending the analysis back to the last one thousand years, the main impact of the radiative forcing is an OHC increase at high latitudes, explained to some extent by a reduction in cloud cover and the subsequent increase of short-wave radiation at the surface. This OHC response is dominated by the effect of volcanism in the preindustrial era, and by the fast increase of GHGs during the last 150 yr. Likewise, salient impacts from internal climate variability are observed at regional scales. For instance, upper temperature in the equatorial Pacific is controlled by ENSO (El Nino Southern Oscillation) variability from interannual to multidecadal timescales. Also, both the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) modulate intermittently the interdecadal OHC variability in the North Pacific and Mid Atlantic, respectively. The NAO, through its influence on North Atlantic surface heat fluxes and convection, also plays an important role on the OHC at multiple timescales, leading first to a cooling in the Labrador and Irminger seas, and later on to a North Atlantic warming, associated with a delayed impact on the AMO.

Stable carbon and oxygen isotope ratios of benthic and planktic foraminifera from the Atlantic Ocean

Benthonic foraminifera in late Pleistocene deep-sea cores show significant variation in delta 13C with depth in sediment. This, and the report by Sommer et al., (in prep) of delta 13C variations in planktonic foraminifera, indicate that the delta13C in dissolved oceanic CO2 undergoes a significant change in a few thousand years. This is in apparent contradiction to the estimated 300 ka residence time for carbon in the ocean. It is suggested that this is a consequence of changes in the terrestrial plant biomass, which has a delta13C of about -25?. Postulated changes in world vegetation, particularly in tropical rainforests during the Late Pleistocene, were sufficient to produce change of the magnitude observed. Rapid expansions of forests between 13 ka and 8 ka ago may have resulted in the striking accumulation of aragonite pteropods in Atlantic Ocean sediments of the age. Rapid deforestation during an interglacial-glacial transition probably caused the intense carbonate dissolution which is observed in Equatorial Pacific Ocean sediments deposited over this interbal. The current rate of injection of fossil fuel CO2 into the atmosphere is substantially greater than the rate at which it was added during post-interglacial aridification in the tropics.

(Table 1) Age determination of Arctic Ocean sediment cores

Accelerator mass spectrometer 14C dated stable isotope data from Neogloboquadrina pachyerma in cores raised from the Mendeleyev Ridge and slope provide evidence for significant influx of meltwater to the western Arctic Ocean during the early part of marine oxygen isotope stage 1 (OIS 1) and during several intervals within OIS 3. The strongest OIS 3 meltwater event occurred before ca. 45 ka (conventional radiocarbon age) and was probably related to the deglaciation at the beginning of OIS 3. Major meltwater input to the western Arctic Ocean during the last deglaciation coincides closely with the maximum rate of global sea-level rise as determined from the Barbados sea-level record, demonstrating a strong link between the global record and changes in the central Arctic Ocean. OIS 2, which includes the last glacial maximum, is very condensed or absent in the cores. Abundance and d13C values for N. pachyderma in the middle part of OIS 3 are similar to modern values, indicating high productivity and seasonal ice-free areas along the Arctic margin at that time. These records indicate that the Arctic Ocean was a source of heat and moisture to the northern polar atmosphere during parts of OIS 3.

Analysis of minerals from Arctic Ocean sediments

The Arctic Ocean System is a key player regarding the climatic changes of Earth. Its highly sensitive ice Cover, the exchange of surface and deep water masses with the global ocean and the coupling with the atmosphere interact directly with global climatic changes. The output of cold, polar water and sea ice influences the production of deep water in the North Atlantic and controls the global ocean circulation ("the conveyor belt"). The Arctic Ocean is surrounded by the large Northern Hemisphere ice sheets which not only affect the sedimentation in the Arctic Ocean but also are supposed to induce the Course of glacials and interglacials. Terrigenous sediment delivered from the ice sheets by icebergs and meltwater as well as through sea ice are major components of Arctic Ocean sediments. Hence, the terrigenous content of Arctic Ocean sediments is an outstanding archive to investigate changes in the paleoenvironment. Glazigenic sediments of the Canadian Arctic Archipelago and surface samples of the Arctic Ocean and the Siberian shelf regions were investigated by means of x-ray diffraction of the bulk fraction. The source regions of distinct mineral compositions were to be deciphered. Regarding the complex circumpolar geology stable christalline shield rocks, active and ancient fold belts including magmatic and metamorphic rocks, sedimentary rocks and wide periglacial lowlands with permafrost provide a complete range of possible mineral combinations. Non- glaciated shelf regions mix the local input from a possible point source of a particular mineral combination with the whole shelf material and function as a sampler of the entire region draining to the shelf. To take this into account, a literature research was performed. Descriptions of outcropping lithologies and Arctic Ocean sediments were scanned for their mineral association. The analyses of glazigenic and shelf sediments yielded a close relationship between their mineral composition and the adjacent source region. The most striking difference between the circumpolar source regions is the extensive outcrop of carbonate rocks in the vicinity of the Canadian Arctic Archipelago and in N Greenland while siliciclastic sediments dominate the Siberian shelves. In the Siberian shelf region the eastern Kara Sea and the western Laptev Sea form a destinct region defined by high smectite, (clino-) pyroxene and plagioclase input. The source of this signal are the extensive outcrops of the Siberian trap basalt in the Putorana Plateau which is drained by the tributaries of the Yenissei and Khatanga. The eastern Laptev Sea and the East Siberian Sea can also be treated as one source region containing a feldspar, quartz, illite, mica, and chlorite asscciation combined with the trace minerals hornblende and epidote. Franz Josef Land provides a mineral composition rich in quartz and kaolinite. The diverse rock suite of the Svalbard archipelago distributes specific mineral compositions of highly metamorphic christalline rocks, dolomite-rich carbonate rocks and sedimentary rocks with a higher diagenetic potential manifested in stable newly built diagenetic minerals and high organic maturity. To reconstruct the last 30,000 years as an example of the transition between glacial and interglacial conditions a profile of sediment cores, recovered during the RV Polarstern" expedition ARK-VIIIl3 (ARCTIC '91), and additional sediment cores around Svalbard were investigated. Besides the mineralogy of different grain size fractions several additional sedimentological and organo-geochemical Parameterswere used. A detailed stratigraphic framework was achieved. By exploiting this data set changes in the mineral composition of the Eurasian Basin sediments can be related to climatic changes. Certain mineral compositions can even be associated with particular transport processes, e.g. the smectitel pyroxene association with sea ice transport from the eastern Kara Sea and the western Laptev Sea. Hence, it is possible to decipher the complex interplay between the influx of warm Atlantic waters into the Southwest of the Eurasian Basin, the waxing and waning of the Svalbard1Barents- Sea- and Kara-Sea-Ice-Sheets, the flooding of the Siberian shelf regions and the surface and deep water circulation. Until now the Arctic Ocean was assumed to be a rather stable System during the last 30,000 years which only switched from a completely ice covered situation during the glacial to seasonally Open waters during the interglacial. But this work using mineral assemblages of sediment cores in the vicinity of Svalbard revealed fast changes in the inflow of warm Atlantic water with the Westspitsbergen Current (< 1000 years), short periods of advances and retreats of the marine based Eurasian ice sheets (1000-3000 years), and short melting phases (400 years?). Deglaciation of the marine-based Eurasian and the land-based north American and Greenland ice sheets are not simultaneous. This thesis postulates that the Kara Sea Ice Sheet released an early meltwater signal prior to 15,000 14C years leading the Barents Sea Ice Sheet while the western land-based ice sheets are following later than 13,500 14C years. The northern Eurasian Basin records the shift between iceberg and sea-ice material derived from the Canadian Arctic Archipelago and N-Greenland and material transported by sea-ice and surface currents from the Siberian shelf region. The phasing of the deglaciation becomes very obvious using the dolomite and quartd phyllosilicate record. It is also supposed that the flooding of the Laptev Sea during the Holocene is manifested in a stepwise increase of sediment input at the Lomonosov Ridge between the Eurasian and Amerasian Basin. Depending on the strength of meltwater pulses from the adjacent ice sheets the Transpolar Drift can probably be relocated. These movements are traceable by the distribution of indicator minerals. Based on the outcome of this work the feasibility of bulk mineral determination can be qualified as excellent tool for paleoenvironmental reconstructions in the Arctic Ocean. The easy preparation and objective determination of bulk mineralogy provided by the QUAX software bears the potential to use this analyses as basic measuring method preceding more time consuming and highly specialised mineralogical investigations (e.g. clay mineralogy, heavy mineral determination).

Fisheries for the future : restructuring the government-industry partnership : national ocean goals and objectives for 1980's

Mode of access: Internet.

Particle size of Saharan dust in the Atlantic Ocean, from October 2012 to November 2013

Mineral dust has a large impact on regional and global climate, depending on its particle size. Especially in the Atlantic Ocean downwind of the Sahara, the largest dust source on earth, the effects can be substantial but are poorly understood. This study focuses on seasonal and spatial variations in particle size of Saharan dust deposition across the Atlantic Ocean, using an array of submarine sediment traps moored along a transect at 12° N. We show that the particle size decreases downwind with increased distance from the Saharan source, due to higher gravitational settling velocities of coarse particles in the atmosphere. Modal grain sizes vary between 4 and 33 µm throughout the different seasons and at five locations along the transect. This is much coarser than previously suggested and incorporated into climate models. In addition, seasonal changes are prominent, with coarser dust in summer, and finer dust in winter and spring. Such seasonal changes are caused by transport at higher altitudes and at greater wind velocities during summer than in winter. Also the latitudinal migration of the dust cloud, associated with the Intertropical Convergence Zone, causes seasonal differences in deposition as the summer dust cloud is located more to the north, and more directly above the sampled transect. Furthermore, increased precipitation and more frequent dust storms in summer coincide with coarser dust deposition. Our findings contribute to understanding Saharan dust transport and deposition relevant for the interpretation of sedimentary records for climate reconstructions, as well as for global and regional models for improved prediction of future climate.

Geological and trace element evidence for a marine sedimentary environment of deposition and biogenicity of 3.45 Ga stromatolitic carbonates in the Pilbara Craton, and support for a reducing Archaean ocean

Bedded carbonate rocks from the 3.45 Ga Warrawoona Group, Pilbara Craton, contain structures that have been regarded either as the oldest known stromatolites or as abiotic hydrothermal deposits. We present new field and petrological observations and high-precision REE + Y data from the carbonates in order to test the origin of the deposits. Trace element geochemistry from a number of laminated stromatolitic dolomite samples of the c. 3.40 Ga Strelley Pool Chert conclusively shows that they precipitated from anoxic seawater, probably in a very shallow environment consistent with previous sedimentological observations. Edge-wise conglomerates in troughs between stromatolites and widespread cross-stratification provide additional evidence of stromatolite construction, at least partly, from layers of particulate sediment, rather than solely from rigid crusts. Accumulation of particulate sediment on steep stromatolite sides in a high-energy environment suggests organic binding of the surface. Relative and absolute REE + Y contents are exactly comparable with Late Archaean microbial carbonates of widely agreed biological origin. Ankerite from a unit of bedded ankerite–chert couplets from near the top of the stratigraphically older (3.49 Ga) Dresser Formation, which immediately underlies wrinkly stromatolites with small, broad, low-amplitude domes, also precipitated from anoxic seawater. The REE + Y data of carbonates from the Strelley Pool Chert and Dresser Formation contrast strongly with those from siderite layers in a jasper–siderite–Fe-chlorite banded iron-formation from the base of the Panorama Formation (3.45 Ga), which is clearly hydrothermal in origin. The geochemical results, together with sedimentological data, strongly support: (1) deposition of Dresser Formation and Strelley Pool Chert carbonates from Archaean seawater, in part as particulate carbonate sediment; (2) biogenicity of the stromatolitic carbonates; (3) a reducing Archaean atmosphere; (4) ongoing extensive terrestrial erosion prior to ∼3.45 Ga.

Correlations between the satellite-derived seasonal cycle of phytoplankton biomass and aerosol optical depth in the Southern Ocean: Evidence for the influence of sea ice

The relationship between the production of dimethylsulfide (DMS) in the upper ocean and atmospheric sulfate aerosols has been confirmed through local shipboard measurements, and global modeling studies alike. In order to examine whether such a connection may be recoverable in the satellite record, we have analyzed the correlation between mean surface chlorophyll (CHL) and aerosol optical depth (AOD) in the Southern Ocean, where the marine atmosphere is relatively remote from anthropogenic and continental influences. We carried out the analysis in 5-degree zonal bands between 50 degrees S and 70 degrees S, for the period ( 1997 - 2004), and in smaller meridional sectors in the Eastern Antarctic, Ross and Weddell seas. Seasonality is moderate to strong in both CHL and AOD signatures throughout the study regions. Coherence in the CHL and AOD time series is strong in the band between 50 degrees S and 60 degrees S, however this synchrony is absent in the sea-ice zone (SIZ) south of 60 degrees S. Marked interannual variability in CHL occurs south of 60 degrees S, presumably related to variability in sea-ice production during the previous winter. We find a clear latitudinal difference in the cross correlation between CHL and AOD, with the AOD peak preceding the CHL bloom by up to 6 weeks in the SIZ. This suggests that substantial trace gas emissions ( aerosol precursors) are being produced over the SIZ in spring ( October - December) as sea ice melts. This hypothesis is supported by field data that record extremely high levels of sulfur species in sea ice, surface seawater, and the overlying atmosphere during ice melt.