Soothsaying DOM: A Current Perspective on the Future of Oceanic Dissolved Organic Carbon

The vast majority of freshly produced oceanic dissolved organic carbon (DOC) is derived from marine phytoplankton, then rapidly recycled by heterotrophic microbes. A small fraction of this DOC survives long enough to be routed to the interior ocean, which houses the largest and oldest DOC reservoir. DOC reactivity depends upon its intrinsic chemical composition and extrinsic environmental conditions. Therefore, recalcitrance is an emergent property of DOC that is analytically difficult to constrain. New isotopic techniques that track the flow of carbon through individual organic molecules show promise in unveiling specific biosynthetic or degradation pathways that control the metabolic turnover of DOC and its accumulation in the deep ocean. However, a multivariate approach is required to constrain current carbon fluxes so that we may better predict how the cycling of oceanic DOC will be altered with continued climate change. Ocean warming, acidification, and oxygen depletion may upset the balance between the primary production and heterotrophic reworking of DOC, thus modifying the amount and/or composition of recalcitrant DOC. Climate change and anthropogenic activities may enhance mobilization of terrestrial DOC and/or stimulate DOC production in coastal waters, but it is unclear how this would affect the flux of DOC to the open ocean. Here, we assess current knowledge on the oceanic DOC cycle and identify research gaps that must be addressed to successfully implement its use in global scale carbon models

Spatial and Temporal Patterns of Pore Water Chemistry in the Inter-Tidal Zone of a High Energy Beach

Submarine groundwater discharge (SGD) is a ubiquitous source of meteoric fresh groundwater and recirculating seawater to the coastal ocean. Due to the hidden distribution of SGD, as well as the hydraulic- and stratigraphy-driven spatial and temporal heterogeneities, one of the biggest challenges to date is the correct assessment of SGD-driven constituent fluxes. Here, we present results from a 3-dimensional seasonal sampling campaign of a shallow subterranean estuary in a high-energy, meso-tidal beach, Spiekeroog Island, Northern Germany. We determined beach topography and analyzed physico-chemical and biogeochemical parameters such as salinity, temperature, dissolved oxygen, Fe(II) and dissolved organic matter fluorescence (FDOM). Overall, the highest gradients in pore water chemistry were found in the cross-shore direction. In particular, a strong physico-chemical differentiation between the tidal high water and low water line was found and reflected relatively stable in- and exfiltrating conditions in these areas. Contrastingly, in between, the pore water compositions in the existing foreshore ridge and runnel system were very heterogeneous on a spatial and temporal scale. The reasons for this observation may be the strong morphological changes that occur throughout the entire year, which affect the exact locations and heights of the ridge and runnel structures and associated flow paths. Further, seasonal changes in temperature and inland hydraulic head, and the associated effect on microbial mediated redox reactions likely overprint these patterns. In the long-shore direction the pore water chemistry varied less than the along the cross-shore direction. Variation in long-shore direction was probably occurring due to topography changes of the ridge-runnel structure and a physical heterogeneity of the sediment, which produced non-uniform groundwater flow conditions. We conclude that on meso-tidal high energy beaches, the rapidly changing beach morphology produces zones with different approximations to steady-state conditions. Therefore, we suggest that zone-specific endmember sampling is the optimal strategy to reduce uncertainties of SGD-driven constituent fluxes

연안 갯벌 해역에서 라듐 추적자를 이용한 해저 지하수 유출량 측정 : 영양염류 플럭스와 생물학적 반응

Thesis(doctors) --서울대학교 대학원 :지구환경과학부,2009.8.Docto

Environmental and DOM FTICRMS data for Spiekeroog Beach

This dataset was acquired to investigate the sources and sinks of dissolved organic matter in a high-energy beach subterranean estuary on Spiekeroog Island, German North Sea. The North Beach sampling location is approximately at 53°46'45N, 7°42'40E. Data were collected during a total of five sampling campaigns in the period of September 2016 - September 2019, spanning over all four seasons. The samples collected were from beach porewaters, seawater, and groundwater from the islands' freshwater lens. Pore water samples were collected with push-point lances (10-100 cm depth), seawater samples with bottles in the surf zone, and groundwater samples from inland monitoring wells (4-40 m depth). Samples were filtered onsite and preserved for storage (acidification for dissolved organic carbon, dissolved organic nitrogen, and trace metals, and poisoning with HgCl2 for dissolved nutrients). In situ data were collected, including temperature, salinity, oxygen concentrations (instrument: WTW Multi 3430), and humic-like fluorescent DOM (instrument: Turner Aquafluor). Laboratory analyses were conducted within a week of sampling and included spectrophotometry for nutrients, ICP-OES for trace metals, and TOC-VCPH analysis for DOC and TDN. Acidified subsamples were desalted and concentrated by solid-phase extraction, then analyzed on via ultra-high resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS on a 15T Bruker solariX XR

Fe- and Cu-complex formation with artificial ligands investigated by ultra-high resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS): Implications for natural metal-organic complex studies

In recent years, electrospray-ionization mass spectrometry (ESI-MS) has been increasingly used to complement the bulk determination of metal-ligand equilibria, for example via competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV). However, ESI-MS speciation analyses may be impacted by instrumental artefacts such as reduction reactions, fragmentation, and adduct formation at the ESI source, changes in the ionization efficiencies of the detected species in relation to sample matrix, and peak overlaps in response to increasing sample complexity. In our study, equilibria of the known artificial ligands citrate, ethylenediaminetetraacetic acid (EDTA), 1-nitroso-2-naphthol (NN), and salicylaldoxime (SA) with iron (Fe) and copper (Cu) were investigated by ultra-high resolution ESI-MS, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), under a variety of sample matrix and ionization settings. The acquired mass spectra were compared with metal-ligand equilibrium data from the literature as well as an adapted speciation model. Overall, the mass spectra produced representative species mentioned in previous reports and predicted by the speciation calculations, such as Fe(Cit), Cu(Cit)2, Fe(EDTA), Cu(EDTA), Fe(NN)3, and Cu(SA)2. The analyses furthermore revealed new species which had been hypothesized but not measured directly using other methods, for example ternary complexes of citrate with Fe and Cu, Cu(SA) monomers, and the dimer Fe(SA)2. Finally, parallel measurements of a Cu+SA calibration series and a Cu+SA+EDTA competition series indicated that FT-ICR-MS can produce linear responses and low detection limits analogous to those of ACSV. We propose that ultra-high resolution FT-ICR-MS can be used as a representative tool to study interactions of trace metals with artificial as well as natural, unknown ligands at the molecular level

Molecular Fractionation of Dissolved Organic Matter in a Shallow Subterranean Estuary : The Role of the Iron Curtain

Iron that precipitates under aerobic conditions in natural aquatic systems scavenges dissolved organic matter (DOM) from solution. Subterranean estuaries (STEs) are of major importance for land−ocean biogeochemical fluxes. Their specific redox boundaries, coined the “iron curtain” due to the abundance of precipitated iron(III) (oxy)hydroxides, are hot spots for the removal and redissolution of iron, associated nutrients, and DOM. We used ultra-high-resolution electro- spray ionization Fourier transform ion cyclotron resonance mass spectrometry to molecularly characterize the iron- coagulating fractions of 32 groundwater and seawater DOM samples along a salinity gradient from a shallow STE on Spiekeroog Island, North Sea, Germany, and linked our findings to trace metal and nutrient concentrations. We found systematic iron coagulation of large (>450 Da), oxygen-rich, and highly aromatic DOM molecules of terrestrial origin. The extent of coagulation increased with growing terrestrial influence along the salinity gradient. Our study is the first to show that the iron curtain may be capable of retaining terrigenous DOM fractions in marine sediments. We hypothesize that the iron curtain serves as an inorganic modulator for the supply of DOM from groundwaters to the sea, and that the STE has the potential to act as a temporal storage or even sink for terrigenous aromatic DOM compounds

DOM molecular composition of porewater collected after incubations

The subterranean estuary (STE) has been recognised as a reactive biogeochemical zone at the groundwater-seawater interface in coastal areas. In this study, we collected sediments from different seasons (April 2021 [storm season) and September 2021 [dry season]) from Mobile Bay, USA. We analysed DOM molecular composition using FTICRMS and microbial assemblages by employing 16S rRNA gene sequencing approach

Physicochemical data of porewater collected after incubations

The subterranean estuary (STE) has been recognised as a reactive biogeochemical zone at the groundwater–seawater interface in coastal areas. In this study, we collected sediments from different seasons (April 2021 [storm season) and September 2021 [dry season]) from Mobile Bay, USA. Shallow sediment cores (up to 2 m) were recovered using a Geoprobe coring system (Model 5410, Geoprobe Systems, Inc.). We conducted controlled laboratory experiments using these sediments and subjected them to various nitrate inputs, salinity regimes, and incubation times. We measured (1) inorganic nutrients (nitrate, nitrite, ammonium, phosphate), (2) dissolved organic carbon (DOC) and nitrogen (DON), (3) total alkalinity

Submarine groundwater discharge from tropical islands: a review

Submarine groundwater discharge (SGD) is a rarely recognized pathway for nutrients and other solutes from land to sea. The sensitive coastal ecosystems around tropical islands could be particularly affected by nutrient discharge associated with SGD in relation to surficial nutrient transport by rivers, but have received comparatively little attention to date. This study reviews the findings of local assessments of submarine groundwater discharge from tropical islands. In addition, the ratio of coast length and land area of individual land bodies is suggested as an appropriate first-order estimate of the relevance of SGD versus river discharge, demonstrating the potential relative importance of SGD from tropical islands over rivers. The review highlights the need for targeted research of submarine groundwater discharge from tropical islands and highlights its relevance for biogeochemical fluxes in these geographic settings