Export of Dissolved Organic Carbon (DOC) compared to the particulate and active fluxes near South Georgia, Southern Ocean

Quantifying the relative contributions of the export of particulate organic carbon (POC), dissolved organic carbon (DOC) and active fluxes by migrating organisms is essential to understand the functioning and vulnerability of the ocean's biological pump. However, these fluxes are rarely measured at the same time. Here we provide a first simultaneous comparison of these biological pump components in the region of South Georgia. We use a combination of in-situ data and an inverse model to calculate the DOC export and the suspended POC export and compare them to the sinking POC and active export. We find that, in this region, the DOC total export contributes about 6.6% (23.0–37.5 mg C m−2 day−1) to the total export flux, the active flux has no discernible contribution, and the sinking POC flux is dominant with a mean value of 409 mg C m−2 day−1. Diapycnal fluxes of DOC obtained from the cruise data constitute only a minor fraction (0.05–1.28 mg C m−2 day−1) of the total DOC export estimated by the inverse model and are exceeded on average by the diapycnal flux of suspended POC. Our results also indicate that the total export of DOC is driven by isopycnal transport. Future fieldwork in the region of South Georgia should focus on quantifying the isopycnal flux of DOC. Future measurement campaigns should also aim to simultaneously measure the particulate, dissolved and active components of the biological pump at contrasting locations and at different times to resolve the variability of their relative contribution

Evidence of nitrification associated with globally distributed pelagic jellyfish

Often considered detrimental to the environment and human activities, jellyfish blooms are increasing in several coastal regions worldwide. Yet, the overall effect of these outbreaks on ecosystem productivity and structure are not fully understood. Here we provide evidence for a so far unanticipated role of jellyfish in marine nitrogen cycling. Pelagic jellyfish release nitrogen as a metabolic waste product in form of ammonium. Yet, we observed high rates of nitrification (NH4+ → NO3−, 5.7–40.8 nM gWW−1 [wet weight] h−1) associated with the scyphomedusae Aurelia aurita, Chrysaora hysoscella, and Chrysaora pacifica and low rates of incomplete nitrification (NH4+ → NO2−, 1.0–2.8 nM gWW−1 h−1) associated with Chrysaora fulgida, C. hysoscella, and C. pacifica. These observations indicate that microbes living in association with these jellyfish thrive by oxidizing the readily available ammonia to nitrite and nitrate. The four studied species have a large geographic distribution and exhibit frequent population outbreaks. We show that, during such outbreaks, jellyfish‐associated release of nitrogen can provide more than 100% of the nitrogen required for primary production. These findings reveal a so far overlooked pathway when assessing pelagic nitrification rates that might be of particular relevance in nitrogen depleted surface waters and at high jellyfish population densities

Enhanced mercury reduction in the South Atlantic Ocean during carbon remineralization

Highlights • Dissolved gaseous mercury can be calculated from modeled dissolved inorganic carbon. • Modeled dissolved gaseous mercury agrees well with worldwide observations. • Dissolved gaseous mercury is related to depth and macronutrients concentrations. Mercury (Hg) in seawater is subject to interconversions via (photo)chemical and (micro)biological processes that determine the extent of dissolved gaseous mercury (DGM) (re)emission and the production of monomethylmercury. We investigated Hg speciation in the South Atlantic Ocean on a GEOTRACES cruise along a 40°S section between December 2011 and January 2012 (354 samples collected at 24 stations from surface to 5250 m maximum depth). Using statistical analysis, concentrations of methylated mercury (MeHg, geometric mean 35.4 fmol L−1) were related to seawater temperature, salinity, and fluorescence. DGM concentrations (geometric mean 0.17 pmol L−1) were related to water column depth, concentrations of macronutrients and dissolved inorganic carbon (DIC). The first-ever observed linear correlation between DGM and DIC obtained from high-resolution data indicates possible DGM production by organic matter remineralization via biological or dark abiotic reactions. DGM concentrations projected from literature DIC data using the newly discovered DGM–DIC relationship agreed with published DGM observations

Physical and biological forcings on the carbonate chemistry in the North Atlantic Ocean

The atmospheric concentration of CO2 has risen considerably since the industrial revolution, and the subsequent uptake of atmospheric CO2 by the oceans has affected the carbonate system and caused a reduction in the pH of the oceans. Model estimates involving future CO2 emission scenarios have predicted a significant increase of oceanic Dissolved Inorganic Carbon concentrations by the end of the century, corresponding to a decrease in oceanic pH by up to 0.4. In order to observe and predict changes in primary productivity and community structure in the oceans associated with future climate change, precise measurements of all the carbonate system parameters are important. The natural processes affecting the seasonal and regional variations of the carbonate chemistry are still poorly understood and sustained monitoring programs are required in order to determine the importance of hydrographical and biogeochemical forcings. The relationships between physical and biological parameters and carbonate system parameters were investigated in several regions of the North Atlantic Ocean, allowing a better understanding of the natural processes affecting the carbonate system in this ocean basin. For this purpose, the seasonal and inter-annual variability of the carbonate system in the Northeast Atlantic Ocean was studied through a ship of opportunity program, allowing observations of the short-term processes affecting the carbonate system and air-sea CO2 fluxes. The results showed contrasting effects of winter mixing and sea surface temperature on the carbonate system and the air-sea CO2 fluxes. In addition, the distributions of the carbonate system parameters were determined in the Iceland Basin and in the sub-tropical Northeast Atlantic Ocean. The carbonate system in the Iceland Basin was characterized by mesoscale variability associated to the presence and development of an eddy dipole in the study region; while the sub-tropical Northeast Atlantic Ocean showed spatial variability in all the chemical parameters, associated with coastal upwelling and remineralization in an oxygen minimum zone. Although the physics appeared to be the main forcing on the carbonate system in this study, the role of biology in the seasonality of the carbonate system is highly important. However, physical forcings tend to set the level for biological drawdown and therefore highly contribute to the variability of the carbonate system and CO2 fluxes

Particulate silica and Si recycling in the surface waters of the Eastern Equatorial Pacific

International audienceThe distributions of biogenic and lithogenic silica concentrations and net silica production rates in the upper 120 m of the Eastern Equatorial Pacific (EEP) were examined in December 2004, on two transects situated at 110°W (4°N to 3°S) and along the equator (110°W to 140°W). Lithogenic silica (lSiO2) was generally <10 nmol Si l−1 with maximum concentrations reaching 25 nmol l−1 in surface waters. These low concentrations confirm low atmospheric inputs of particulate Si, consistent with reported low inputs of wind-borne material in the EEP. In spite of active upwelling of silicic acid-rich waters the biogenic silica (bSiO2) concentrations were generally low, falling between 100 and 180 nmol Si l−1 in the upper 50 m and decreasing to less than 50 nmol Si l−1 below ∼90 m. Estimates of net bSiO2 production rates revealed that the rate of production exceeded that of dissolution in the upper euphotic layer (0-40 m) along 110°W with net production extending somewhat deeper (60-100 m) to the west along the equator. Net production rates in the surface layer were low, ranging between 5 and 40 nmol Si l−1 d−1, consistent with previous observations that diatoms are small contributors to autotrophic biomass in the EEP. Net silica dissolution predominated in the lower euphotic layer (40-120 m), indicating active Si recycling which diminished the strength of the silica pump in this region

Evidence of nitrification associated with globally distributed pelagic jellyfish

Bioavailable nitrogen is a scarce resource in most of the surface oceanand often limits primary productivity. Although Pelagic jellyfish excretesubstantial amounts of ammonia (the preferred form of nitrogen formost phytoplankton), they are overlooked players in marine nitrogencycling. Here, we observed high rates of nitrification (NH4+ → NO3-, 5.7– 40.8 nM gWW-1 (wet weight) h-1) associated with the scyphomedusaeAurelia aurita, Chrysaora hysoscella and Chrysaora pacifica and low ratesof incomplete nitrification (NH4+ → NO2-, 1-2.7 nM gWW-1 h-1)associated with Chrysaora fulgida, Chrysaora hysoscella and Chrysaorapacifica. These observations indicate that microbes living in associationwith the jellyfish thrive by oxidizing the readily available ammonia tonitrite and nitrate. The four studied species are abundant over a largegeographic distribution and exhibit frequent population outbreaks. Weshow that, during such outbreaks, jellyfish-associated release of nitrogencan provide more than 100% of the nitrogen required for primaryproduction. These findings reveal a so far overlooked pathway whenassessing pelagic nitrification rates that might be of particular relevancein nitrogen depleted surface waters and at high jellyfish populationdensities

Acoustic backscatter data from two visits to site P3 (P3A and P3B) during COMICS cruise DY086 in November to December, 2017

Acoustic backscatter data was collected at five frequencies (18, 38, 70, 120 and 200 kHz) across two visits to site P3, South Georgia, aboard the RRS Discovery during DY086. Acoustic backscatter was measured with the Simrad EK60. The data consistently shows no evidence of synchronised diel vertical migration

Starlikeness of Libera transformation (II) (Applications of Complex Function Theory to Differential Equations)

The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges. The IDP2017 is the result of a truly international effort involving 326 researchers from 25 countries. This publication provides the critical reference for unpublished data, as well as for studies that make use of a large cross-section of data from the IDP2017. This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González