Dissolved Organic Carbon in the North Atlantic Meridional Overturning Circulation

The quantitative role of the Atlantic Meridional Overturning Circulation (AMOC) in dissolved organic carbon (DOC) export is evaluated by combining DOC measurements with observed water mass transports. In the eastern subpolar North Atlantic, both upper and lower limbs of the AMOC transport high-DOC waters. Deep water formation that connects the two limbs of the AMOC results in a high downward export of non-refractory DOC (197 Tg-C·yr-1). Subsequent remineralization in the lower limb of the AMOC, between subpolar and subtropical latitudes, consumes 72% of the DOC exported by the whole Atlantic Ocean. The contribution of DOC to the carbon sequestration in the North Atlantic Ocean (62 Tg-C·yr-1) is considerable and represents almost a third of the atmospheric CO 2 uptake in the region

A global database of dissolved organic matter (DOM) concentration measurements in coastal waters (CoastDOM v1)

Measurements of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) con-centrations are used to characterize the dissolved organic matter (DOM) pool and are important components ofbiogeochemical cycling in the coastal ocean. Here, we present the first edition of a global database (CoastDOMv1; available at https://doi.org/10.1594/PANGAEA.964012, L\uf8nborg et al., 2023) compiling previously pub-lished and unpublished measurements of DOC, DON, and DOP in coastal waters. These data are complementedby hydrographic data such as temperature and salinity and, to the extent possible, other biogeochemical variables(e.g. chlorophyll a, inorganic nutrients) and the inorganic carbon system (e.g. dissolved inorganic carbon andtotal alkalinity). Overall, CoastDOM v1 includes observations of concentrations from all continents. However,most data were collected in the Northern Hemisphere, with a clear gap in DOM measurements from the SouthernHemisphere. The data included were collected from 1978 to 2022 and consist of 62 338 data points for DOC,20 356 for DON, and 13 533 for DOP. The number of measurements decreases progressively in the sequenceDOC > DON > DOP, reflecting both differences in the maturity of the analytical methods and the greater focuson carbon cycling by the aquatic science community. The global database shows that the average DOC concen-tration in coastal waters (average \ub1 standard deviation (SD): 182 \ub1 314 μmol C L−1; median: 103 μmol C L−1) is13-fold higher than the average coastal DON concentration (13.6 \ub1 30.4 μmol N L−1; median: 8.0 μmol N L−1),which is itself 39-fold higher than the average coastal DOP concentration (0.34 \ub1 1.11 μmol P L−1; median:0.18 μmol P L−1). This dataset will be useful for identifying global spatial and temporal patterns in DOM and willhelp facilitate the reuse of DOC, DON, and DOP data in studies aimed at better characterizing local biogeochem-ical processes; closing nutrient budgets; estimating carbon, nitrogen, and phosphorous pools; and establishing abaseline for modelling future changes in coastal waters

Chemical tracer transport in the eastern boundary current system of the North Atlantic

The MedBox region, comprising the Strait of Gibraltar to 22ºW and from 24ºN to 41ºN, has been defined using thermohaline and chemical data from three WOCE cruises conducted in 1997/98. The water mass structure of the region was objectively solved by an extended optimum multiparameter (OMP) analysis. Volume transports were estimated from field data and an inverse box model that ensures volume conservation and no deep water formation within the region. The combination of the volume transports, the OMP water mass analysis, and the distributions of chemical parameters allowed for the assessment of the oxygen, inorganic carbon, nitrate, phosphate, and silicate transport mechanisms, their vertical and lateral variability, and the relative contribution of the different water masses in the mid-latitudes of the eastern North Atlantic to these transports. La región MedBox comprende desde el Estrecho de Gibraltar hasta 22ºW y entre 24ºN y 41ºN.

On the variation of alkalinity during phytoplankton photosynthesis

The alkalinity of the organic constituents of marine phytoplankton and their participation in the total alkalinity (TA) change of seawater during photosynthesis are carefully assessed. Quantification of the contribution of phytoplankton chlorophyll, proteins and phosphorus compounds to the hydrogen ion balance of seawater in terms of total inorganic nitrogen (∆[NT] = ∆NH4 +] + ∆[N2] + ∆[NO2–] + ∆[NO3–]) and total inorganic phosphorus (∆[PT]) changes during photosynthesis yielded that the organic components of marine phytoplankton are alkaline by –0.06 ×  ∆[NT] – 0.49 × ∆[PT], and that the potential total alkalinity (TAP) during photosynthesis is TAP = TA – [NH4– + 0.93 × [NO2–] + [NO3–] + 0.08 × [NT] + 0.23 × [PT] for unfiltered seawater samples and TAP = TA – [NH4–] + 0.93 × [NO2–] + [NO3–] + 0.02 × [NT] + 0.26 × [PT] for filtered seawater samples. These equations correct the traditionally used expression TAP = TA + [NO3–]. The TAP anomalies are produced, in order of increasing importance, by N2 fixation, DMSP production and CaCO3 fixation

A global database of dissolved organic matter (DOM) measurements in coastal waters (CoastDOM v1)

The measurements of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) are used to characterize the dissolved organic matter (DOM) pool and are important components of biogeochemical cycling in the coastal ocean. Here, we present the first edition of a global database (CoastDOM v1; available at https://figshare.com/s/512289eb43c4f8e8eaef) compiling previously published and unpublished measurements of DOC, DON, and DOP collected in coastal waters. These data are complemented by hydrographic data such as temperature and salinity and, to the extent possible, other biogeochemical variables (e.g., Chlorophyll-a, inorganic nutrients) and the inorganic carbon system (e.g., dissolved inorganic carbon and total alkalinity). Overall, CoastDOM v1 includes observations from all continents however, most data were collected in the Northern Hemisphere, with a clear gap in coastal water DOM measurements from the Southern Hemisphere. The data included were collected from 1978 to 2022 and consist of 62339 data points for DOC, 20360 for DON and 13440 for DOP. The number of measurements decreases progressively in the sequence DOC > DON > DOP, reflecting both differences in the maturity of the analytical methods and the greater focus on carbon cycling by the aquatic science community. The global database shows that the average DOC concentration in coastal waters (average (standard deviation; SD): 182 (314) \ub5mol C L−1; median: 103 \ub5mol C L−1), is 13-fold greater than the average coastal DON concentrations (average (SD): 13.6 (30.4) \ub5mol N L−1; median: 8.0 \ub5mol N L−1), which was itself 39-fold greater than the average coastal DOP concentrations (average (SD): 0.34 \ub1 1.11 \ub5mol P L−1; median: 0.18 \ub5mol P L−1). This dataset will be useful to identify global spatial and temporal patterns in DOM and to facilitate reuse of DOC, DON and DOP data in studies aimed at better characterising local biogeochemical processes, closing nutrient budgets, estimating carbon, nitrogen and phosphorous pools, as well as identifying a baseline for modelling future changes in coastal waters