ALBERT

Description: 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. Data sets in this collection provide methodological and environmental context to all samples collected during the Tara Oceans Expedition (2009-2013).

Description: Coccolithophores -single-celled calcifying phytoplankton- are an important group of marine primary producers and the dominant builders of calcium carbonate globally. Coccolithophores form extensive blooms and increase the density and sinking speed of organic matter via calcium carbonate ballasting. Thereby, they play a key role in the marine carbon cycle. Coccolithophore physiological responses to experimental ocean acidification have ranged from moderate stimulation to substantial decline in growth and calcification rates, combined with enhanced malformation of their calcite platelets. Here we report on a mesocosm experiment conducted in a Norwegian fjord in which we exposed a natural plankton community to a wide range of CO2-induced ocean acidification, to test whether these physiological responses affect the ecological success of coccolithophore populations. Under high-CO2 treatments, Emiliania huxleyi, the most abundant and productive coccolithophore species, declined in population size during the pre-bloom period and lost the ability to form blooms. As a result, particle sinking velocities declined by up to 30% and sedimented organic matter was reduced by up to 25% relative to controls. There were also strong reductions in seawater concentrations of the climate-active compound dimethylsulfide in CO2-enriched mesocosms. We conclude that ocean acidification can lower calcifying phytoplankton productivity, potentially creating a positive feedback to the climate system.

Description: This collection contains four datasets on (1) chlorophyll a and phaeopigment concentrations, (2) nitrogen and organic carbon contents, (3) sediment oxygen uptakes and benthic boundary fluxes at the sediment-water interface and (4) macrofaunal abundance and biodiversity in sediments in the Canadian Arctic in 2008 and 2009. Data have been produced for a PhD thesis based on samples taken during the following expeditions: - Circumpolar Flaw Lead Study, Legs 9-10 - ArcticNet expedition 2008, Leg 11 (http://www.arcticnet.ulaval.ca/docs/2008_Amundsen_Expedition_Report.pdf) - ArcticNet expedition 2009, Leg 4 (http://www.arcticnet.ulaval.ca/docs/2009_Amundsen_Expedition_Report.pdf) - Malina expedition 2009 (Malina http://malina.obs-vlfr.fr/index.html; http://www.arcticnet.ulaval.ca/docs/2009_Amundsen_Expedition_Report.pdf) In general, sediment retrieved with a giant box corer were used to determine benthic boundary fluxes (oxygen, silicic acid, phosphate, nitrate, ammonium) in incubation chambers, as well as sediment pigment concentration from seperate cores, to study the effect of environmental conditions on benthic ecosystem functions. Parts of the data available in this collection have been analysed for addressing various ecological questions in spatial and temporal context in the publications listed below. A general description of the study region can be found in Link et al. 2013 (POne). Please download the metadata and methods file for more details.

Description: The particulate export of photosynthetically fixed carbon from the surface ocean to the ocean interior is a key component of the biological carbon pump and, by extension, of the global carbon cycle. An extensively applied method to estimate the downward flux of particulate carbon is the ²³⁴Th technique, which uses the deficit of ²³⁴Th with respect to its parent, ²³⁸U, coupled with the C/²³⁴Th ratios measured in sinking. More than two decades have passed since the ²³⁴Th technique was first applied to determine the export flux of particulate carbon but the C/²³⁴Th ratio on sinking particles remains as one of the principal uncertainties of this approach. Here we present a global database of 9110 C/²³⁴Th ratios collected using in situ pumps, sediment traps and bottles. Ratios have been grouped, based on the particle size or the device used for the sampling, as: i) Large particles ii) Small particles, iii) Sediment traps and iv) Bulk. The samples were collected between 1989 and 2016 and are distributed among most of the open ocean Longhurst provinces, with some coastal areas also represented. As expected, the data are not evenly distributed along the water column, with most of the data points found in the upper 100-200 m, although the depth range expands from surface down to 〉5500 m. Globally, the ratios range from 0.012 to 1778 µmol/dpm. This database shows how particulate C/²³⁴Th ratios vary with time, depth, particle size and location, which is important for the application of the ²³⁴Th approach and the estimate of the global magnitude of the biological carbon pump.

Description: The human-induced rise in atmospheric carbon dioxide since the industrial revolution has led to increasing oceanic carbon uptake and changes in seawater carbonate chemistry, resulting in lowering of surface water pH. In this study we investigated the effect of increasing CO2 partial pressure (pCO2) on concentrations of volatile biogenic dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP), through monoculture studies and community pCO2 perturbation. DMS is a climatically important gas produced by many marine algae: it transfers sulfur into the atmosphere and is a major influence on biogeochemical climate regulation through breakdown to sulfate and formation of subsequent cloud condensation nuclei (CCN). Overall, production of DMS and DMSP by the coccolithophore Emiliania huxleyi strain RCC1229 was unaffected by growth at 900 µatm pCO2, but DMSP production normalised to cell volume was 12 % lower at the higher pCO2 treatment. These cultures were compared with community DMS and DMSP production during an elevated pCO2 mesocosm experiment with the aim of studying E. huxleyi in the natural environment. Results contrasted with the culture experiments and showed reductions in community DMS and DMSP concentrations of up to 60 and 32 % respectively at pCO2 up to 3000 µatm, with changes attributed to poorer growth of DMSP-producing nanophytoplankton species, including E. huxleyi, and potentially increased microbial consumption of DMS and dissolved DMSP at higher pCO2. DMS and DMSP production differences between culture and community likely arise from pH affecting the inter-species responses between microbial producers and consumers.

Description: Photosynthetic parameters for the TRANSSIZ expedition aboard the RV Polarstern (PS92, ARK-XXIX/1) between the 19th of May and the 26th June of 2015.