Multinet and water column properties of station SO225-21

Insight into past changes of upper ocean stratification, circulation, and nutrient signatures rely on our knowledge of the apparent calcification depth (ACD) and ecology of planktonic foraminifera, which serve as archives for paleoceanographic relevant geochemical signals. The ACD of different species varies strongly between ocean basins, but also regionally. We constrained foraminiferal ACDs in the western Pacific warm pool (Manihiki Plateau) by comparing stable oxygen and carbon isotopes (d18Ocalcite, d13Ccalcite) as well as Mg/Ca ratios from living planktonic foraminifera to in-situ physical and chemical water mass properties (temperature, salinity, d18Oseawater, d13CDIC). Our analyses point to Globigerinoides ruber as the shallowest dweller, followed by Globigerinoides sacculifer, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata and Globotaloides hexagonus inhabiting increasingly greater depths. These findings are consistent with other ocean basins; however, absolute ACDs differ from other studies. The uppermost mixed-layer species G. ruber and G. sacculifer denote mean calcification depths of ~95 m and ~120 m, respectively. These Western Pacific ACDs are much deeper than in most other studies and most likely relate to the thick surface mixed layer and the deep chlorophyll maximum in this region. Our results indicate that N. dutertrei appears to be influenced by mixing waters from the Pacific equatorial divergence, while P. obliquiloculata with an ACD of ~160 m is more suitable for thermocline reconstructions. ACDs of G. hexagonus reveal a deep calcification depth of ~450 m in oxygen-depleted, but nutrient-rich water masses, consistent to other studies. As the d13C of G. hexagonus is in near-equilibrium with ambient seawater, we suggest this species is suitable for tracing nutrient conditions in equatorial water masses originating in extra-topical regions.

Properties of seawater and particulate matter from a WETLabs AC-S spectrophotometer and a WETLabs chlorophyll fluorometer mounted on the continuous surface water sampling system during the Tara Oceans expedition 2009-2013

The Tara Oceans Expedition (2009-2013) was a global survey of ocean ecosystems aboard the Sailing Vessel Tara. It carried out extensive measurements of evironmental conditions and collected plankton (viruses, bacteria, protists and metazoans) for later analysis 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 publication provides permanent links to original and updated versions of validated data files containing measurements from the Continuous Surface Sampling System [CSSS]. Water was pumped at the front of the vessel from ~2m depth, then de-bubbled and circulated to a WETLabs AC-S spectrophotometer and a WETLabs chlorophyll fluorometer. Systems maintenance (instrument cleaning, flushing) was done approximately once a week and in port between successive legs. All data were stamped with a GPS.

Molecular dissolved organic matter composition in lakes across Sweden as relative intensities of FT-ICR-MS peaks and PARAFAC components and optical indices

Whether intrinsic molecular properties or extrinsic factors such as environmental conditions control the decomposition of natural organic matter across soil, marine and freshwater systems has been subject to debate. Comprehensive evaluations of the controls that molecular structure exerts on organic matter's persistence in the environment have been precluded by organic matter's extreme complexity. Here we examine dissolved organic matter from 109 Swedish lakes using ultrahigh-resolution mass spectrometry and optical spectroscopy to investigate the constraints on its persistence in the environment. We find that degradation processes preferentially remove oxidized, aromatic compounds, whereas reduced, aliphatic and N-containing compounds are either resistant to degradation or tightly cycled and thus persist in aquatic systems. The patterns we observe for individual molecules are consistent with our measurements of emergent bulk characteristics of organic matter at wide geographic and temporal scales, as reflected by optical properties. We conclude that intrinsic molecular properties are an important control of overall organic matter reactivity.

Contiunous surface water uncorrected and quench-corrected active fluorescence and derived chlorophyll a concentration using calibration by HPLC pigments during POLARSTERN cruise ANT-XXV/1

The relationship between phytoplankton assemblages and the associated optical properties of the water body is important for the further development of algorithms for large-scale remote sensing of phytoplankton biomass and the identification of phytoplankton functional types (PFTs), which are often representative for different biogeochemical export scenarios. Optical in-situ measurements aid in the identification of phytoplankton groups with differing pigment compositions and are widely used to validate remote sensing data. In this study we present results from an interdisciplinary cruise aboard the RV Polarstern along a north-to-south transect in the eastern Atlantic Ocean in November 2008. Phytoplankton community composition was identified using a broad set of in-situ measurements. Water samples from the surface and the depth of maximum chlorophyll concentration were analyzed by high performance liquid chromatography (HPLC), flow cytometry, spectrophotometry and microscopy. Simultaneously, the above- and underwater light field was measured by a set of high spectral resolution (hyperspectral) radiometers. An unsupervised cluster algorithm applied to the measured parameters allowed us to define bio-optical provinces, which we compared to ecological provinces proposed elsewhere in the literature. As could be expected, picophytoplankton was responsible for most of the variability of PFTs in the eastern Atlantic Ocean. Our bio-optical clusters agreed well with established provinces and thus can be used to classify areas of similar biogeography. This method has the potential to become an automated approach where satellite data could be used to identify shifting boundaries of established ecological provinces or to track exceptions from the rule to improve our understanding of the biogeochemical cycles in the ocean.

Objective Mapping of Argo data in the Weddell Gyre: a gridded dataset of upper ocean water properties, link to data files in NetCDF format

The Weddell Gyre plays a crucial role in the regulation of climate by transferring heat into the deep ocean through deep and bottom water mass formation. However, our understanding of Weddell Gyre water mass properties is limited to regions of data availability, primarily along the Prime Meridian. The aim is to provide a dataset of the upper water column properties of the entire Weddell Gyre. Objective mapping was applied to Argo float data in order to produce spatially gridded, time composite maps of temperature and salinity for fixed pressure levels ranging from 50 to 2000 dbar, as well as temperature, salinity and pressure at the level of the sub-surface temperature maximum. While the data are currently too limited to incorporate time into the gridded structure, the data are extensive enough to produce maps of the entire region across three time composite periods (2002-2005, 2006-2009 and 2010-2013), which can be used to determine how representative conclusions drawn from data collected along general RV transect lines are on a gyre scale perspective. The time composite data sets are provided as netCDF files; one for each time period. Mapped fields of conservative temperature, absolute salinity and potential density are provided for 41 vertical pressure levels. The above variables as well as pressure are provided at the level of the sub-surface temperature maximum. Corresponding mapping errors are also included in the netCDF files. Further details are provided in the global attributes, such as the unit variables and structure of the corresponding data array (i.e. latitude x longitude x vertical pressure level). In addition, all files ending in "_potTpSal" provide mapped fields of potential temperature and practical salinity.

Properties of water masses, taxa abundance, and isotopic ratios of samples obtained around Svalbard archipelago

The feeding strategies of Calanus hyperboreus, C. glacialis, and C. finmarchicus were investigated in the high-Arctic Svalbard region (77-81 °N) in May, August, and December, including seasons with algal blooms, late- to post-bloom situations, and unproductive winter periods. Stable isotope and fatty acid trophic marker (FATM) techniques were employed together to assess trophic level (TL), carbon sources (phytoplankton vs. ice algae), and diet of the three Calanus species. In addition, population development, distribution, and nutritional state (i.e. storage lipids) were examined to estimate their population status at the time of sampling. In May and August, the vertical distribution of the three Calanus species usually coincided with the maximum algal biomass. Their stable isotope and fatty acid (FA) composition indicated that they all were essentially herbivores in May, when the algal biomass was highest. Their FA composition, however, revealed different food preferences. C. hyperboreus had high proportions of 18:4n3, suggesting that it fed mainly on Phaeocystis, whereas C. glacialis and C. finmarchicus had high proportions of 16:4n1, 16:1n7, and 20:5n3, suggesting diatoms as their major food source. Carbon sources (i.e. phytoplankton vs. ice algae) were not possible to determine solely from FATM techniques since ice-diatoms and pelagic-diatoms were characterised by the same FA. However, the enriched d13C values of C. glacialis and C. finmarchicus in May indicated that they fed both on pelagic- and ice-diatoms. Patterns in absolute FA and fatty alcohol composition revealed that diatoms were the most important food for C. hyperboreus and C. glacialis, followed by Phaeocystis, whereas diatoms, Phaeocystis and other small autotrophic flagellates were equally important food for C. finmarchicus. During periods of lower algal biomass, only C. glacialis exhibited evidence of significant dietary switch, with a TL indicative of omnivory (mean TL=2.4). Large spatial variability was observed in population development, distribution, and lipid store sizes in August. At the northernmost station at the southern margin of the Arctic Ocean, the three Calanus species had similarly low lipid stores as they had in May, suggesting that they ascended later in the year. In December, relatively lipid-rich specimens had TL similar to those during the peak productive season (TL~2.0), suggesting that they were hibernating and not feeding on the available refractory material available at that time of the year. In contrast, lipid-poor specimens in December had substantially high TL (TL=2.5), suggesting that they were active and possibly were feeding.

Bottom water properties observed during Nathanial B. Palmer cruises NBP00-08 and NBP04-08 to the Southern Ocean

We report on observations of dense shelf water overflows and Antarctic Bottom Water (AABW) formation along the continental margin of the Adelie and George V Land coast between 140°E and 149°E. Vertical sections and bottom layer water mass properties sampled during two RVIB Nathaniel B Palmer hydrographic surveys (NBP00-08, December 2000/January 2001 and NBP04-08, October 2004) describe the spreading of cold, dense shelf water on the continental slope and rise from two independent source regions. The primary source region is the Adelie Depression, exporting high-salinity dense shelf water through the Adelie Sill at 143°E. An additional eastern source region of lower-salinity dense shelf water from the Mertz Depression is identified for the first time from bottom layer properties northwest of the Mertz Sill and Mertz Bank (146°E-148°E) that extend as far as the Buffon Channel (144.75°E) in summer. Regional analysis of satellite-derived ice production estimates over the entire region from 1992 to 2005 suggests that up to 40% of the total ice production for the region occurs over the Mertz Depression and therefore this area is likely to make a significant contribution to the total dense shelf water export. Concurrent time series from bottom-mounted Microcats and ADCP instruments from the Mertz Polynya Experiment (April 1998 to May 1999) near the Adelie Sill and on the upper continental slope (1150 m) and lower continental rise (3250 m) to the north describe the seasonal variability in downslope events and their interaction with the ambient water masses. The critical density for shelf water to produce AABW is examined and found to be 27.85 kg/m**3 from the Adelie Depression and as low as 27.80 kg/m**3 from the Mertz Depression. This study suggests previous dense shelf water export estimates based on the flow through the Adelie Sill alone are conservative and that other regions around East Antarctica with similar ice production to the Mertz Depression could be contributing to the total AABW in the Australian-Antarctic Basin.

The CoastColour Round Robin datasets: a database to evaluate the performance of algorithms for the retrieval of water quality parameters in coastal waters

The CoastColour project Round Robin (CCRR) project (http://www.coastcolour.org) funded by the European Space Agency (ESA) was designed to bring together a variety of reference datasets and to use these to test algorithms and assess their accuracy for retrieving water quality parameters. This information was then developed to help end-users of remote sensing products to select the most accurate algorithms for their coastal region. To facilitate this, an inter-comparison of the performance of algorithms for the retrieval of in-water properties over coastal waters was carried out. The comparison used three types of datasets on which ocean colour algorithms were tested. The description and comparison of the three datasets are the focus of this paper, and include the Medium Resolution Imaging Spectrometer (MERIS) Level 2 match-ups, in situ reflectance measurements and data generated by a radiative transfer model (HydroLight). The datasets mainly consisted of 6,484 marine reflectance associated with various geometrical (sensor viewing and solar angles) and sky conditions and water constituents: Total Suspended Matter (TSM) and Chlorophyll-a (CHL) concentrations, and the absorption of Coloured Dissolved Organic Matter (CDOM). Inherent optical properties were also provided in the simulated datasets (5,000 simulations) and from 3,054 match-up locations. The distributions of reflectance at selected MERIS bands and band ratios, CHL and TSM as a function of reflectance, from the three datasets are compared. Match-up and in situ sites where deviations occur are identified. The distribution of the three reflectance datasets are also compared to the simulated and in situ reflectances used previously by the International Ocean Colour Coordinating Group (IOCCG, 2006) for algorithm testing, showing a clear extension of the CCRR data which covers more turbid waters.