The German Bight (southern North Sea) receives nutrients, dissolved organic matter (DOM), and trace metals via rivers and tide-driven submarine groundwater discharge (SGD). However, deciphering DOM sources and transformations in highly dynamic coastal settings remains challenging. We present a study assessing the different marine, riverine, and porewater (sulfidic) sources and characterizing molecular transformations of solid-phase extracted (SPE) DOM in the German North Sea using ultrahigh-resolution mass spectrometry (FT-ICR-MS), in combination with quantitative dissolved organic sulfur (DOS), and dissolved black carbon (DBC), as well as with dissolved trace metal (Ba, Co, Fe, Gd, Mo, Mn, W), and dissolved nutrient (nitrite, nitrate, phosphate, silicate) data. Despite the importance of rivers, porewater outwelling was a major source for dissolved nutrients, and several trace metals as well as potentially recalcitrant DOM (DOS) to the southern North Sea. Riverine DOS was amended by (sulfidic) porewater discharge as revealed by non-conservative behavior of elemental carbon-to-sulfur ratios and sulfur-content of molecular formulae (from FT-ICR-MS). Discharging oxygen-depleted porewater was a source for dissolved phosphate, whereas dissolved Mn and Si were removed in the German Bight which was probably due to precipitation as Mn(hydr)oxides and biological uptake, respectively. We show that porewater discharge must be considered in addition to riverine sources to understand the complex interplay of DOM, nutrient, and trace metal transformations in coastal ecosystems.

Primary Presenter: Michael Seidel, University of Oldenburg (m.seidel@uni-oldenburg.de)

Authors:

Michael Seidel, University of Oldenburg  (m.seidel@uni-oldenburg.de)

Linn Speidel, ETH Zürich  (linn.speidel@erdw.ethz.ch)

Roger Carvalho da Silva, University of Oldenburg  (roger.carvalho.da.silva1@uni-oldenburg.de)

Melanie Beck, University of Oldenburg  (melanie.beck@uni-oldenburg.de)

Olaf Dellwig, Leibniz-Institute for Baltic Sea Research  (olaf.dellwig@io-warnemuende.de)

Jochen Wollschläger, University of Oldenburg  (jochen.wollschlaeger@uni-oldenburg.de)

Thorsten Dittmar, University of Oldenburg  (thorsten.dittmar@uni-oldenburg.de)