Removal of Refractory Dissolved Organic Carbon in the Amundsen Sea, Antarctica.

The removal mechanism of refractory deep-ocean dissolved organic carbon (deep-DOC) is poorly understood. The Amundsen Sea Polynya (ASP) serves as a natural test basin for assessing the fate of deep-DOC when it is supplied with a large amount of fresh-DOC and exposed to strong solar radiation during the polynya opening in austral summer. We measured the radiocarbon content of DOC in the water column on the western Amundsen shelf. The radiocarbon content of DOC in the surface water of the ASP reflected higher primary production than in the region covered by sea ice. The radiocarbon measurements of DOC, taken two years apart in the ASP, were different, suggesting rapid cycling of DOC. The increase in DOC concentration was less than expected from the observed increase in radiocarbon content from those at the greatest depths. Based on a radiocarbon mass balance, we show that deep-DOC is consumed along with fresh-DOC in the ASP. Our observations imply that water circulation through the surface layer, where fresh-DOC is produced, may play an important role in global DOC cycling

Submarine groundwater discharge: updates on its measurement techniques, geophysical drivers, magnitudes, and effects

The number of studies concerning Submarine Groundwater Discharge (SGD) grew quickly as we entered the twenty-first century. Many hydrological and oceanographic processes that drive and influence SGD were identified and characterized during this period. These processes included tidal effects on SGD, water and solute fluxes, biogeochemical transformations through the subterranean estuary, and material transport via SGD from land to sea. Here we compile and summarize the significant progress in SGD assessment methodologies, considering both the terrestrial and marine driving forces, and local as well as global evaluations of groundwater discharge with an emphasis on investigations published over the past decade. Our treatment presents the state-of-the-art progress of SGD studies from geophysical, geochemical, bio-ecological, economic, and cultural perspectives. We identify and summarize remaining research questions, make recommendations for future research directions, and discuss potential future challenges, including impacts of climate change on SGD and improved estimates of the global magnitude of SGD

Incidence of harmful algal blooms in pristine subtropical ocean: a satellite remote sensing approach (Jeju Island)

Despite the increasing numbers of red tide events in the pristine subtropical ocean, a paucity of previous observations has limited understanding of harmful algae in the seas around the Korean Peninsula. Therefore, using six years (2012–2017) of Geostationary Ocean Color Imager (GOCI) satellite data, we characterized the red tides around Jeju Island, a volcanic island located near the paths of the Jeju Warm Current and Tsushima Warm Current, using the Normalized Red Tide Index (NRTI) method. The seawater around Jeju Island has for a long time been considered to be very clear, with relatively low suspended particulate matter concentrations and few harmful algae. Nonetheless, the satellite-based NRTI detection method used in this study detected and supported the existence of red tides in the coastal region around Jeju Island. Analysis of the red tide distribution showed that red tide first began to appear near the western coast of Jeju Island, then developed in the northern and eastern coastal regions, and finally vanished in the eastern coastal region. The monthly averages of the NRTI demonstrated a bloom event from April to May in every year. Additional fall blooms were detected in August–September, particularly in 2013 and 2016. The NRTI revealed strong interannual variations. The longest blooms occurred in 2015, and the most comprehensive and strongest event occurred in the spring of 2016. The latter three years (2015–2017) had much higher NRTI than the former three years (2012–2014). The probability of red tide occurrence at a given point during the 6-year study period revealed spatial differences. Relatively high probability of 0.3–0.5 was determined along the northern coastal region, whereas low probability of less than 0.2 was found along the southern region. Ground truth data also showed more frequent observations and higher red tide cell densities along the northern coast. Changes in NRTI in spring are positively correlated with changes in ENSO indices in winter. This study is the first to use a satellite-based approach with a vast long-term satellite database to elucidate the existence and probability of red tides near Jeju Island. We anticipate that this study will provide a useful strategy for remote monitoring of harmful algal blooms over wide regions using optical data

Intercalibration studies of \u3csup\u3e210\u3c/sup\u3ePo and \u3csup\u3e210\u3c/sup\u3ePb in dissolved and particulate seawater samples

Documented is an intercalibration (IC) exercise for both 210Po and 210Pb in seawater aliquots distributed between up to eight international laboratories that followed individual protocols. Dissolved and particulate samples were provided by GEOTRACES during two IC cruises at baseline stations in the North Atlantic and North Pacific oceans. Included were surface and/or deep dissolved and particulate samples at each site, plus complete profiles analyzed by the laboratory of the lead author. An unspecified solid phase standard was also distributed with 210Po and 210Pb in secular equilibrium to confirm spike calibrations. The 210Po activities reported n = 8) for the standard were very similar with a relative standard deviation (RSD) of 3.6% and mean value indistinguishable from the certified value, confirming accurate calibration of Po spikes. For seawater samples, the agreement was strongly dependent for both nuclides on the activity of the samples. The agreement was relatively good for dissolved seawater samples (RSD = 9% to 29%, n = 4), moderate for the particulate samples (RSD = 12% to 80%, n = 8), and poor for particulate dip blanks (RSD = 50% to 200%, n = 8). Noted is the higher apparent affinity of 210Po versus 210Pb for polysulphone filter material. Some lack of reproducibility between labs may have been caused by unspecified differences in individual lab protocols and calculations. A minimum sample activity of 0.1 dpm for both nuclides is recommended for an adequate reproducible sample activity. It is suggested that a consistent set of procedures and calculations be used to optimize future 210Po and 210Pb analyses in seawater samples

Global estimate of submarine groundwater discharge based on an observationally constrained radium isotope model

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 41 (2014): 8438–8444, doi:10.1002/2014GL061574.Along the continental margins, rivers and submarine groundwater supply nutrients, trace elements, and radionuclides to the coastal ocean, supporting coastal ecosystems and, increasingly, causing harmful algal blooms and eutrophication. While the global magnitude of gauged riverine water discharge is well known, the magnitude of submarine groundwater discharge (SGD) is poorly constrained. Using an inverse model combined with a global compilation of 228Ra observations, we show that the SGD integrated over the Atlantic and Indo-Pacific Oceans between 60°S and 70°N is (12 ± 3) × 1013 m3 yr−1, which is 3 to 4 times greater than the freshwater fluxes into the oceans by rivers. Unlike the rivers, where more than half of the total flux is discharged into the Atlantic, about 70% of SGD flows into the Indo-Pacific Oceans. We suggest that SGD is the dominant pathway for dissolved terrestrial materials to the global ocean, and this necessitates revisions for the budgets of chemical elements including carbon.This work was supported by the Ministry of Oceans and Fisheries, Korea, through the Korea Institute of Marine Science and Technology (KIMST) (20120176) and National Research Foundation (NRF) of Korea (2013R1A2A1A05004343 and 2013R1A1A1058203). Charette and Moore's contributions were supported by the US National Science Foundation through the GEOTRACES project

The release of dissolved actinium to the ocean : A global comparison of different end-members

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 109 (2008): 409-420, doi:10.1016/j.marchem.2007.07.005.The measurement of short-lived 223Ra often involves a second measurement for supported activities, which represents 227Ac in the sample. Here we exploit this fact, presenting a set of 284 values on the oceanic distribution of 227Ac, which was collected when analyzing water samples for short-lived radium isotopes by the radium delayed coincidence counting system. The present work compiles 227Ac data from coastal regions all over the northern hemisphere, including values from ground water, from estuaries and lagoons, and from marine endmembers. Deep-sea samples from a continental slope off Puerto Rico and from an active vent site near Hawaii complete the overview of 227Ac near its potential sources. The average 227Ac activities of nearshore marine end-members range from 0.4 dpm * m-3 at the Gulf of Mexico to 3.0 dpm *m-3 in the coastal waters of the Korean Strait. In analogy to 228Ra, we find the extension of adjacent shelf regions to play a substantial role for 227Ac activities, although less pronounced than for radium, due to its weaker shelf source. Based on previously published values, we calculate an open ocean 227Ac inventory of 1.35 * 1018 dpm 227Acex in the ocean, which corresponds to 37 moles, or 8.4 kg. This implies a flux of 127 dpm*m-2*y-1 from the deep-sea floor. For the shelf regions, we obtain a global inventory of 227Ac of 4.5 * 1015 dpm, which cannot be converted directly into a flux value, as the regional loss term of 227Ac to the open ocean would have to be included. Ac has so far been considered to behave similarly to Ra in the marine environment, with the exception of a strong Ac source in the deep-sea due to 231Paex. Here, we present evidence of geochemical differences between Ac, which is retained in a warm vent system, and Ra, which is readily released (Moore et al., submitted). Another potential mechanism of producing deviations in 227Ac/228Ra and daughter isotope ratios from the expected production value of lithogenic material is observed at reducing environments, where enrichment in uranium may occur. The presented data here may serve as a reference for including 227Ac in circulation models, and the overview provides values for some end-members that contribute to the global Ac distribution

Measurement and Application of Radium and Radon in the Environment

The measurement of low-level Ra and Rn isotopes in water samples has become increasingly convenient and accurate in recent years. I summarize these new and advanced techniques and then introduce their application fields in geophysical and environmental studies

The significant inputs of trace elements and rare earth elements from melting glaciers in Antarctic coastal waters

To evaluate the impact of modern glacier melting on the chemical enrichment of Antarctic coastal waters, we measured trace elements, including dissolved iron (Fe) and rare earth elements (REEs), together with dissolved inorganic nitrogen, phosphorous, silicate and dissolved organic carbon (DOC) in ice, snow and coastal seawater of Marian Cove in the northernmost part of Antarctica (62°S). There was an increase in the concentrations of Fe and other trace elements (Al, Mn, Cr, Ni, Co, Pb and REEs) between the bay mouth and the glacier valleys. Good correlations between salinity and these chemical elements indicate that the trend was mainly due to the influence of glacier meltwater (GMW). When the effect of GMW was quantified based on plots of its presence (average 5.7%) in the surface water of the cove, the concentrations of trace elements in seawater increased 18-fold for Fe, eight- to 10-fold for Al and Mn and up to four-fold for Cr, Ni, Co, Pb and REEs by GMW. However, the contribution of GMW to inorganic nutrients and DOC was negligible. The significance of GMW-borne REE contribution in this cove was further evidenced by middle REE enrichment in cove water. Our results suggest that the currently increasing glacier melting in Antarctica has a significant influence on the level of trace elements, particularly Fe, in cove water, which in turn may have a significant impact on the biogeochemistry of coastal seawater in Antarctica.Keywords: Iron; trace elements; rare earth elements; glacier melting; Antarctica; Marian Cove.(Published: 7 May 2015)Citation: Polar Research 2015, 34, 24289, http://dx.doi.org/10.3402/polar.v34.2428

Atmospheric depositional fluxes of trace elements, 210 Pb, and 7 Be to the Sargasso Sea

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