The volume of earth's ocean

Author Posting. © Oceanography Society, 2010. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 23, no. 2 (2010): 112-114.Despite playing a significant role in the global water cycle, ocean volume has not been re-examined in over 25 years. The main uncertainty associated with ocean volume is the mean ocean depth. The earliest studies tended to overestimate ocean depth due to undersampling of seamounts and ocean ridges. The advent of the echosounder in the 1920s and subsequent ship-borne technologies rapidly increased aerial coverage of the ocean; hence, over time there has been a gradual decrease in calculated mean ocean depth. Today, however, in situ measurements span only ~ 10% of the ocean’s surface area. Here, we use satellite altimetry data to estimate the ocean’s volume, which is lower by a volume equivalent to 500 times the Great Lakes or five times the Gulf of Mexico when compared to the most recent published estimates.This work was funded in part by the EarthWater Institute (http://www. earthwaterinstitute.org) in concert with the institute’s ongoing Global Water Audit

Climate-driven sea level anomalies modulate coastal groundwater dynamics and discharge

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 2701–2706, doi:10.1002/grl.50192.To better understand the physical drivers of submarine groundwater discharge (SGD) in the coastal ocean, we conducted a detailed field and modeling study within an unconfined coastal aquifer system. We monitored the hydraulic gradient across the coastal aquifer and movement of the mixing zone over multiple years. At our study site, sea level dominated over groundwater head as the largest contributor to variability in the hydraulic gradient and therefore SGD. Model results indicate the seawater recirculation component of SGD was enhanced during summer while the terrestrial component dominated during winter due to seasonal changes in sea level driven by a combination of long period solar tides, temperature and winds. In one year, sea level remained elevated year round due to a combination of ENSO and NAO climate modes. Hence, predicted changes in regional climate variability driven sea level may impact future rates of SGD and biogeochemical cycling within coastal aquifers.This work is a result of research sponsored by the NSF Chemical Oceanography program (OCE- 0425061 to M.C. and A.M. and OCE-0751525 to M.C.) and an NDSEG graduate fellowship (to M.G.).2013-12-0

An inverse relationship between production and export efficiency in the Southern Ocean

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 1557–1561, doi:10.1002/grl.50219.In the past two decades, a number of studies have been carried out in the Southern Ocean to look at export production using drifting sediment traps and thorium-234 based measurements, which allows us to reexamine the validity of using the existing relationships between production, export efficiency, and temperature to derive satellite-based carbon export estimates in this region. Comparisons of in situ export rates with modeled rates indicate a two to fourfold overestimation of export production by existing models. Comprehensive analysis of in situ data indicates two major reasons for this difference: (i) in situ data indicate a trend of decreasing export efficiency with increasing production which is contrary to existing export models and (ii) the export efficiencies appear to be less sensitive to temperature in this region compared to the global estimates used in the existing models. The most important implication of these observations is that the simplest models of export, which predict increase in carbon flux with increasing surface productivity, may require additional parameters, different weighing of existing parameters, or separate algorithms for different oceanic regimes.This work was supported by NASA award number NNX08AB48G.2013-10-2

Unexpected source of Fukushima-derived radiocesium to the coastal ocean of Japan

Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 114 (2017): 11092-11096, doi:10.1073/pnas.1708659114.There are 440 operational nuclear reactors in the world, with approximately half situated along the coastline. This includes the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), which experienced multiple reactor meltdowns in March 2011 followed by the release of radioactivity to the marine environment. While surface inputs to the ocean via atmospheric deposition and rivers are usually well monitored after a nuclear accident, no study has focused on subterranean pathways. During our study period, we found the highest cesium-137 (137Cs) levels (up to 23,000 Bq m-3) outside of the FDNPP site not in the ocean, rivers or potable groundwater, but in groundwater beneath sand beaches over tens of kilometers away from the FDNPP. Here, we present evidence of a previously unknown, ongoing source of Fukushima-derived 137Cs to the coastal ocean. We postulate that these beach sands were contaminated in 2011 through wave and tide driven exchange and sorption of highly radioactive Cs from seawater. Subsequent desorption of 137Cs and fluid exchange from the beach sands was quantified using naturally occurring radium isotopes. This estimated ocean 137Cs source (0.6 TBq y-1) is of similar magnitude as the ongoing releases of 137Cs from the FDNPP site for 2013-2016, as well as the input of Fukushima-derived dissolved 137Cs via rivers. Though this ongoing source is not at present a public health issue for Japan, the release of Cs of this type and scale needs to be considered in NPP monitoring and scenarios involving future accidents.V. Sanial was supported by a Postdoctoral Scholarship from the Center for Marine and Environmental Radioactivity (CMER). Funding for this work was provided by the Gordon and Betty Moore Foundation, the Deerbrook Charitable Trust, as well as the EC 7th Framework project COMET-FRAME (COordination and iMplementation of a pan-Europe instrumenT for radioecology) and KAKENHI (24110008)

Coupled radon, methane and nitrate sensors for large-scale assessment of groundwater discharge and non-point source pollution to coastal waters

Author Posting. © The Author(s), 2009. 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 Journal of Environmental Radioactivity 101 (2010): 553-563, doi:10.1016/j.jenvrad.2009.12.004.We constructed a survey system of radon/methane/nitrate/salinity to find sites of submarine groundwater discharge (SGD) and groundwater nitrate input. We deployed the system in Waquoit Bay and Boston Harbor, MA where we derived SGD rates using a mass balance of radon with methane serving as a fine resolution qualitative indicator of groundwater. In Waquoit Bay we identified several locations of enhanced groundwater discharge, out of which two (Childs and Quashnet Rivers) were studied in more detail. The Childs River was characterized by high nitrate input via groundwater discharge, while the Quashnet River SGD was notable but not a significant source of nitrate. Our radon survey of Boston Harbor revealed several sites with significant SGD, out of these Inner Harbor and parts of Dorchester Bay and Quincy Bay had groundwater fluxes accompanied by significant water column nitrogen concentrations. The survey system has proven effective in revealing areas of SGD and non-point source pollution.R. Camilli acknowledges the National Ocean Partnership Program (NOPP) for supporting the development of the TETHYS mass spectrometer through research grant #OCE-0537173. H. Dulaiova, M. A. Charette and R. Camilli acknowledge funding support from the WHOI Coastal Institute and MIT Sea Grant College Program under NOAA grant number NA06OAR4170019, project number 5710002173. H. Dulaiova was funded by the WHOI Academic Program’s postdoctoral scholarship

Relationship between water and aragonite barium concentrations in aquaria reared juvenile corals

This paper is not subject to U.S. copyright. The definitive version was published in Geochimica et Cosmochimica Acta 209 (2017): 123-134, doi:10.1016/j.gca.2017.04.006.Coral barium to calcium (Ba/Ca) ratios have been used to reconstruct records of upwelling, river and groundwater discharge, and sediment and dust input to the coastal ocean. However, this proxy has not yet been explicitly tested to determine if Ba inclusion in the coral skeleton is directly proportional to seawater Ba concentration and to further determine how additional factors such as temperature and calcification rate control coral Ba/Ca ratios. We measured the inclusion of Ba within aquaria reared juvenile corals (Favia fragum) at three temperatures (∼27.7, 24.6 and 22.5 °C) and three seawater Ba concentrations (73, 230 and 450 nmol kg−1). Coral polyps were settled on tiles conditioned with encrusting coralline algae, which complicated chemical analysis of the coral skeletal material grown during the aquaria experiments. We utilized Sr/Ca ratios of encrusting coralline algae (as low as 3.4 mmol mol−1) to correct coral Ba/Ca for this contamination, which was determined to be 26 ± 11% using a two end member mixing model. Notably, there was a large range in Ba/Ca across all treatments, however, we found that Ba inclusion was linear across the full concentration range. The temperature sensitivity of the distribution coefficient is within the range of previously reported values. Finally, calcification rate, which displayed large variability, was not correlated to the distribution coefficient. The observed temperature dependence predicts a change in coral Ba/Ca ratios of 1.1 μmol mol−1 from 20 to 28 °C for typical coastal ocean Ba concentrations of 50 nmol kg−1. Given the linear uptake of Ba by corals observed in this study, coral proxy records that demonstrate peaks of 10–25 μmol mol−1 would require coastal seawater Ba of between 60 and 145 nmol kg−1. Further validation of the coral Ba/Ca proxy requires evaluation of changes in seawater chemistry associated with the environmental perturbation recorded by the coral as well as verification of these results for Porites species, which are widely used in paleo reconstructions.M.E.G. was supported by a NDSEG graduate fellowship. Funding for this research came from the NSF Chemical Oceanography program (OCE-0751525) and the Coastal Ocean Institute, the Ocean and Climate Change Institute and the Ocean Ventures Fund at Woods Hole Oceanographic Institution

Seasonal cycle of circulation in the Antarctic Peninsula and the off-shelf transport of shelf waters into southern Drake Passage and Scotia Sea

Author Posting. © The Author(s), 2013. 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 Deep Sea Research Part II: Topical Studies in Oceanography 90 (2013): 15-30, doi:10.1016/j.dsr2.2013.02.029.The seasonal cycle of circulation and transport in the Antarctic Peninsula shelf region is investigated using a high-resolution (~2km) regional model based on the Regional Oceanic Modeling System (ROMS). The model also includes a naturally occurring tracer with a strong source over the shelf (radium isotope 228Ra, t1/2=5.8 year) to investigate the sediment Fe input and its transport. The model is spun up for three years using climatological boundary and surface forcing and then run for the 2004-2006 period using realistic forcing. Model results suggest a persistent and coherent circulation system throughout the year consisting of several major components that converge water masses from various sources toward Elephant Island. These currents are largely in geostrophic balance, driven by surface winds, topographic steering, and large-scale forcing. Strong off-shelf transport of the Fe-rich shelf waters takes place over the northeastern shelf/slope of Elephant Island, driven by a combination of topographic steering, extension of shelf currents, and strong horizontal mixing between the ACC and shelf waters. These results are generally consistent with recent and historical observational studies. Both the shelf circulation and off-shelf transport show a significant seasonality, mainly due to the seasonal changes of surface winds and large-scale circulation. Modeled and observed distributions of 228Ra suggest that a majority of Fe-rich upper layer waters exported off-shelf around Elephant Island are carried by the shelfbreak current and the Bransfield Strait Current from the shallow sills between Gerlache Strait and Livingston Island, and northern shelf of the South Shetland Islands, where strong winter mixing supplies much of the sediment derived nutrients (including Fe) input to the surface layer.This project is supported by NOAA grant NA09OAR4310062. MZ and MJ 11 are also supported by NSF grant 0948378 and MAC by NSF grant 0948442

Revisiting \u3csup\u3e228\u3c/sup\u3eTh as a Tool for Determining Sedimentation and Mass Accumulation Rates

The use of 228Th has seen limited application for determining sedimentation and mass accumulation rates in coastal and marine environments. Recent analytical advances have enabled rapid, precise measurements of particle-bound 228Th using a radium delayed coincidence counting system (RaDeCC). Herein we review the 228Th cycle in the marine environment and revisit the historical use of 228Th as a tracer for determining sediment vertical accretion and mass accumulation rates in light of new measurement techniques. Case studies comparing accumulation rates from 228Th and 210Pb are presented for a micro-tidal salt marsh and a marginal sea environment. 228Th and 210Pb have been previously measured in mangrove, deltaic, continental shelf and ocean basin environments, and a literature synthesis reveals that 228Th (measured via alpha or gamma spectrometry) derived accumulation rates are generally equal to or greater than estimates derived from 210Pb, reflecting different integration periods. Use of 228Th is well-suited for shallow (\u3c15 cm) cores over decadal timescales. Application is limited to relatively homogenous sediment profiles with minor variations in grain size and minimal bioturbation. When appropriate conditions are met, complimentary use of 228Th and 210Pb can demonstrate that the upper layers of a core are undisturbed and can improve spatial coverage in mapping accumulation rates due to the higher sample throughput for sediment 228Th

Kinetics of thorium and particle cycling along the U.S. GEOTRACES North Atlantic Transect

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 125 (2017): 106-128, doi:10.1016/j.dsr.2017.05.003.The high particle reactivity of thorium has resulted in its widespread use in tracing processes impacting marine particles and their chemical constituents. The use of thorium isotopes as tracers of particle dynamics, however, largely relies on our understanding of how the element scavenges onto particles. Here, we estimate apparent rate constants of Th adsorption (k1), Th desorption (k−1), bulk particle degradation (β-1), and bulk particle sinking speed (w) along the water column at 11 open-ocean stations occupied during the GEOTRACES North Atlantic Section (GA03). First, we provide evidence that the budgets of Th isotopes and particles at these stations appear to be generally dominated by radioactive production and decay sorption reactions, particle degradation, and particle sinking. Rate parameters are then estimated by fitting a Th and particle cycling model to data of dissolved and particulate 228,230,234Th, 228Ra, particle concentrations, and 234,238U estimates based on salinity, using a nonlinear programming technique. We find that the adsorption rate constant (k1) generally decreases with depth across the section: broadly, the time scale 1/k1 averages 1.0 yr in the upper 1000 m and (1.4–1.5) yr below. A positive relationship between k1 and particle concentration (P) is found, i.e., , k1 ∝ Pb where b ≥ 1, consistent with the notion that k1 increases with the number of surface sites available for adsorption. The rate constant ratio, K = k1/(k-1 + β-1), which measures the collective influence of rate parameters on Th scavenging, averages 0.2 for most stations and most depths. We clarify the conditions under which K/P is equivalent to the distribution coefficient, KD, test that the conditions are met at the stations, and find that decreases with P, in line with a particle concentration effect (dKD/dP < 0). In contrast to the influence of colloids as envisioned by the Brownian pumping hypothesis, we provide evidence that the particle concentration effect arises from the joint effect of P on the rate constants for thorium attachment to, and detachment from, particles.We acknowledge the U.S. National Science Foundation for providing funding for this study (grant OCE-1232578) and for U.S. GEOTRACES North Atlantic section ship time, sampling, and data analysis. The U.S. NSF also supported the generation of 230Th data (OCE-0927064 to LDEO, OCE-O092860 to WHOI, and OCE-0927754 to UMN) and 228,234Th data (OCE-0925158 to WHOI)