Down-core distribution of live and dead benthic foraminifera in deep sea sediments from the Weddell Sea and the Californian continental borderland

Five short cores sub-sampled from box cores from three sites in the eastern Weddell Sea off Antarctica and in the eastern Pacific off southern California, covering a range in water depth from 500 to 2000 m, were analysed for the down-core distribution of live (stained with Rose Bengal) and dead benthic foraminifera. In the California continental borderland, Planulina ariminensis, Rosalina columbiensis and Trochammina spp. live attached to agglutinated polychaetes tubes that rise above the sedimentwater interface. Bolivina spissa lives exclusively in or on the uppermost sediment. Stained specimens of Chilostomella ovoidea are found down to 6 cm within the sediment and specimens of Globobulimina pacifica down to a maximum of 8 cm. Delta13C values of live G. pacifica decrease with increasing depth from the sediment surface down to 7 cm core depth, indicating that this infaunal species utilizes13C-depleted carbon from pore waters. In the dead, predominantly calcareous benthic forminiferal assemblage, selective dissolution of small delicate tests in the upper sediment column causes a continuous variation in species proportions. In the eastern Weddell Sea, the calcareous Bulimina aculeata lives in a carbonate corrosive environment exclusively in or on the uppermost sediment. The arenaceous Cribrostomoides subglobosum, Recurvoides contortus and some Reophax species are frequently found within the top 4 cm of the sediment, whereas stained specimens of Haplophragmoides bradyi, Glomospira charoides and Cribrostomoides wiesneri occur in maximum abundance below the uppermost 1.5 cm. Species proportions in the dead, predominantly arenaceous, benthic foraminiferal assemblage change in three distinct steps. The first change is caused by calcite dissolution at the sediment-water interface, the second coincides with the lower boundary of intense bioturbation, and the third results from the geochemical shift from oxidizing to reducing conditions below a compacted ash layer.

Properties of seawater (partial pressure of carbon dioxide (pCO2)) from a ProOceanus CO2-Pro sensor mounted on the continuous surface water sampling system during the Tara Oceans expedition 2009-2013

The Tara Oceans Expedition (2009-2013) sampled the world oceans on board a 36 m long schooner, collecting environmental data and organisms from viruses to planktonic metazoans for later analyses using modern sequencing and state-of-the-art imaging technologies. Tara Oceans Data are particularly suited to study the genetic, morphological and functional diversity of plankton. The present data set provides continuous measurements of partial pressure of carbon dioxide (pCO2), using a ProOceanus CO2-Pro instrument mounted on the flowthrough system. This automatic sensor is fitted with an equilibrator made of gas permeable silicone membrane and an internal detection loop with a non-dispersive infrared detector of PPSystems SBA-4 CO2 analyzer. A zero-CO2 baseline is provided for the subsequent measurements circulating the internal gas through a CO2 absorption chamber containing soda lime or Ascarite. The frequency of this automatic zero point calibration was set to be 24 hours. All data recorded during zeroing processes were discarded with the 15-minute data after each calibration. The output of CO2-Pro is the mole fraction of CO2 in the measured water and the pCO2 is obtained using the measured total pressure of the internal wet gas. The fugacity of CO2 (fCO2) in the surface seawater, whose difference with the atmospheric CO2 fugacity is proportional to the air-sea CO2 fluxes, is obtained by correcting the pCO2 for non-ideal CO2 gas concentration according to Weiss (1974). The fCO2 computed using CO2-Pro measurements was corrected to the sea surface condition by considering the temperature effect on fCO2 (Takahashi et al., 1993). The surface seawater observations that were initially estimated with a 15 seconds frequency were averaged every 5-min cycle. The performance of CO2-Pro was adjusted by comparing the sensor outputs against the thermodynamic carbonate calculation of pCO2 using the carbonic system constants of Millero et al. (2006) from the determinations of total inorganic carbon (CT ) and total alkalinity (AT ) in discrete samples collected at sea surface. AT was determined using an automated open cell potentiometric titration (Haraldsson et al. 1997). CT was determined with an automated coulometric titration (Johnson et al. 1985; 1987), using the MIDSOMMA system (Mintrop, 2005). fCO2 data are flagged according to the WOCE guidelines following Pierrot et al. (2009) identifying recommended values and questionable measurements giving additional information about the reasons of the questionability.

Continuous measurements at Schwingbachtal Studienlandschaft in the growing seasons 2013-2014

The recent development of in-situ monitoring devices, such as UV-spectrometers, makes the study of short-term stream chemistry variation relevant, especially the study of diurnal cycles, which are not yet fully understood. Our study is based on high-frequency data from an agricultural catchment (Studienlandschaft Schwingbachtal, Germany). We propose a novel approach, i.e. the combination of cluster analysis and Linear Discriminant Analysis, to mine from these data nitrate behavior patterns. As a result, we observe a seasonality of nitrate diurnal cycles, that differs from the most common cycle seasonality described in the literature, i.e. pre-dawn peaks in spring. Our cycles appear in summer and the maximum and minimum shift to a later time in late summer/autumn. This is observed both for water- and energy-limited years, thus potentially stressing the role of evapotranspiration. This concluding hypothesis on the role of evapotranspiration on nitrate stream concentration, which was obtained through data mining, broadens the perspective on the diurnal cycling of stream nitrate concentrations.

Sediment color variation in laminated Holocene sediments of ODP Site 178-1098

Continuous sediment color records with a resolution of one measurement per millimeter were generated for Site 1098 (Palmer Deep, Antarctic Peninsula) from digital images of the core surfaces to test if the laminated intervals at this site will allow for analysis of high-frequency climate variability in the Circum-Antarctic. Long-term variation in color values correlates with gamma-ray attenuation bulk density. Darker colors are found in laminated intervals with lower bulk density, high biogenic silica, and high total organic carbon content. Darker color values result from the addition of dark laminae to background sediments that show little variation in color. The thicknesses of dark and light laminae were measured in the top 25 meters composite depth to determine the temporal resolution of the laminae. The alternation between dark, biogenic-rich laminae and background sediment essentially represents an annual cycle, but the sediment is not consistently varved. The modal thickness of light laminae is close to the long-term average annual accumulation rate, and results indicate that approximately half of the dark/light couplets in distinctly laminated intervals represent a single year. Missing biogenic laminae are interpreted to represent reduced primary productivity during cold years with delayed breakup of the sea-ice cover.

Latitudinal variation in the planktic foraminifer Contusotruncana contusa in the terminal Cretaceous ocean

The morphological variability (coiling properties, size and shape) of the planktic foraminifer Contusortuncana contusa (Cushman) in the terminal Cretaceous ocean was examined at eight deep-sea sites and two continental sections from low (16°) to middle (42°) paleolatitudes in both hemispheres. The material used in this study includes samples from the South Atlantic (DSDP Sites 356, 527 and 525A), North Atlantic (Sites 384 and 548A), Indian and Pacific Oceans (DSDP Site 465A and ODP Sites 761C and 762C) and Tethyan Ocean (outcrop sections from El-Kef and Caravaca). On average 45 specimens from two samples per location were analysed, from an interval corresponding approximately to the last 60 kyr of the Cretaceous. No differences in coiling direction (dextral proportions were > 90% in all samples), percentage of kummerform specimens (usually > 50%) and number of chambers in the last whorl (4-5) were observed between the sites. Both test size (expressed as spiral outline area and test volume) and total number of chambers increase significantly towards lower latitudes. Similarly, test conicity, examined by shape coordinate and eigenshape methods, and angularity of the spiral outline show a rather continuous, slight increase towards lower latitudes. Kummerform specimens of C. contusa were slightly larger and more conical than normalforms and possessed substantially more chambers (both totally and in the last whorl). A principal components analysis of the sample means of five variables describing size and shape clearly distinguished high-latitude sites (525A, 527, 548A, 761C and 762C) from low-latitude sites (384, 465A, Caravaca and El-Kef). Specimens from Site 356 are transitional with respect to those two groups. The results indicate: (1) considerable morphological variation in C. contusa during the terminal Cretaceous comparable to that known in many Recent planktic foraminiferal species and (2) a geographical distribution of this variation corresponding to previously suggested biogeographic schemes based on quantitative analysis of planktic foraminiferal assemblages. Despite the differences in sample means, the overall morphology of C. contusa overlaps among the sites studied, supporting the classification of all C. contusa morphotypes as a single species. Similarly, no discrete morphologic groups could be distinguished within any of the samples.

Continuous measurement of carbon dioxid partial pressure in seawater in the region of the Iceland-Faroe Ridge (Table 1)

During the 14th expedition of the research vessel "Meteor" from the 2nd of July to the 7th of August 1968 continously recording instruments for measuring the CO2 partial pressure of seawater and atmospheric CO2 were developped by the Meteorological Institute, University of Frankfurt/M. During the Faroer expedition instrumental constants, such as relative and absolute accuracy, inertia and solvent power were tested. The performance of discontinous analyses of water samples was adopted to shipboard conditiones and correction factors depending on water volume, depth of sampling and water temperature were measured. After having computed average values of the continous records (atmosp. CO2 content, CO2 partial pressure, water temperature) geographical distribution, diurnal variation and dependence of diurnal averages were tested. At four different locations CO2 partial pressure was measured in various depths. During the voyage from the Faroer islands to Helgoland the measured concentrations of atmospheric CO2 content and CO2 partial pressure were tested with respect to a correlation of the geographical latitude.