Shipboard flow injection analyis (FIA) of dissolved Al, Fe, and Mn from R/V Knorr cruise KN204-01 (GA03) in the Subtropical northern Atlantic Ocean in 2011 (U.S. GEOTRACES NAT project)

Dataset: GT11 - FIA-AlFeMnShipboard flow injection analyis (FIA) of dissolved Al, Fe, and Mn from R/V Knorr cruise KN204-01 (GA03) in the Subtropical northern Atlantic Ocean in 2011 as part of the U.S. GEOTRACES North Atlantic project. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/3822NSF Division of Ocean Sciences (NSF OCE) OCE-0928741, NSF Division of Ocean Sciences (NSF OCE) OCE-113781

Shipboard flow injection analyis (FIA) of dissolved Al and Fe from R/V Knorr cruise KN199-04 (GA03) in the Subtropical northern Atlantic Ocean in 2010 (U.S. GEOTRACES NAT project)

Dataset: GT10 - FIA-AlFeShipboard flow injection analyis (FIA) of dissolved Al and Fe from R/V Knorr cruise KN199-04 (GA03) in the Subtropical northern Atlantic Ocean in 2010 as part of the U.S. GEOTRACES North Atlantic project. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/3821NSF Division of Ocean Sciences (NSF OCE) OCE-092874

Dissolved Al in the zonal N Atlantic section of the US GEOTRACES 2010/2011 cruises and the importance of hydrothermal inputs

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 116 (2015): 176-186, doi:10.1016/j.dsr2.2014.07.006.The distribution of dissolved aluminium determined during GA03, the US GEOTRACES North Atlantic Transects (US GT NAZT) shows large inputs to the basin from three main sources, atmospheric deposition, outflow from the Mediterranean, and inputs from hydrothermal sources along the Mid Atlantic Ridge (MAR). The partial dissolution of atmospheric aerosols emanating from the Sahara yield high concentrations of dissolved Al in the surface waters of the basin and are used to estimate the geographical pattern of dust deposition. The Mediterranean outflow delivers a large source of dissolved Al to the intermediate waters of the eastern basin and its subsequent distribution within the basin can be explained by simple isopycnal mixing with surrounding water masses. Hydrothermal venting at the Trans-Atlantic Geotraverse (TAG) hydrothermal field in the MAR produces a neutrally buoyant plume that introduces copious quantities of dissolved Al (with concentrations of up to 40nM) to the deeper waters of the North Atlantic that can be seen advecting to the west of the MAR. The concentration of dissolved Al in the deep waters of the eastern basin of the Atlantic can be accounted for by admixing the MAR Al enriched plume water and Antarctic Bottom Water (AABW) as they pass through the Vema Fracture Zone. The data sets show no evidence for biological remineralisation of dissolved Al from Si carrier phases in deep waters.This work was supported by NSF OCE-0928741 and OCE-1137812 to CIM

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

Global estimates of mineral dust aerosol iron and aluminum solubility that account for particle size using diffusion-controlled and surface-area-controlled approximations

Mineral aerosol deposition is recognized as the dominant source of iron to the open ocean and the solubility of iron in the dust aerosol is highly variable, with measurements ranging from 0.01–80%. Global models have difficulty capturing the observed variations in solubility, and have ignored the solubility dependence on aerosol size. We introduce two idealized physical models to estimate the size dependence of mineral aerosol solubility: a diffusion‐controlled model and a surface‐area‐controlled model. These models produce differing time‐ and space‐varying solubility maps for aerosol Fe and Al given the dust age at deposition, size‐resolved dust entrainment fields, and the aerosol acidity. The resulting soluble iron deposition fluxes are substantially different, and more realistic, than a globally uniform solubility approximation. The surface‐area‐controlled solubility varies more than the diffusion‐controlled solubility and better captures the spatial pattern of observed solubility in the Atlantic. However, neither of these two models explains the large solubility variation observed in the Pacific. We then examine the impacts of spatially variable, size‐dependent solubility on marine biogeochemistry with the Biogeochemical Elemental Cycling (BEC) ocean model by comparing the modeled surface ocean dissolved Fe and Al with observations. The diffusion‐based variable solubility does not significantly improve the simulation of dissolved Fe relative to a 5% globally uniform solubility, while the surface‐area‐based variable solubility improves the simulation in the North Atlantic but worsens it in the Pacific and Indian Oceans

Estimating iron and aluminum removal rates in the eastern equatorial Pacific Ocean using a box model approach.

a b s t r a c t Iron limitation plays an important role in maintaining the high-nitrate low-chlorophyll (HNLC) condition in the equatorial upwelling zone. The rate and depth of upwelling control Fe supply to the euphotic zone. This study constrains the transport fluxes and budget of two trace metals, Fe and Al, in the upper ocean. They are co-delivered to the eastern equatorial Pacific surface waters via the Equatorial Undercurrent and upwelling but show distinct biogeochemical cycling processes. We combine the results of the in situ measurements of dissolved Fe and Al (dFe and dAl) with the modeled velocity fields to calculate the physical fluxes. The model calculations are evaluated with the conservation of heat, volume transport, NO 3 and Si(OH) 4 budgets for the equatorial Pacific. The vertical flux due to upwelling provides averaged dFe and dAl supply rates of 1.45 mmol m , respectively. These estimates are equal to the net biological and chemical removal rates of dFe and dAl. The calculated dFe:C net removal ratio is in the range of 3-9 mmol:mol, which agrees with most other estimates. This suggests that the majority of net dFe removal is due to biological uptake in the upper water column. The results of this box model approach illustrate the usefulness of combining the modeled outputs and in situ measurements, which provide additional constraints on Fe transport and cycling in the equatorial Pacific and possibly other HNLC regions

Winter mesoscale circulation on the shelf slope region of the southern Drake Passage

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): 4-14, doi:10.1016/j.dsr2.2013.03.041.An austral winter cruise in July-August 2006 was conducted to study the winter circulation and iron delivery processes in the Southern Drake Passage and Bransfield Strait. Results from current and hydrographic measurements revealed a circulation pattern similar to that of the austral summer season observed in previous studies: The Shackleton Transverse Ridge (STR) in the southern Drake Passage blocks a part of the eastward Antarctic Circumpolar Current (ACC) which forces the ACC to detour southward, produces a Taylor Column over the STR, and forms an ACC jet within the Shackleton Gap, a deep channel between the STR and the shelf of Elephant Island. Observations show that to the west of the STR, the Upper Circumpolar Deep Water (UCDW) intruded onto the shelf around the South Shetland Islands while to the east of the STR, shelf waters were transported off the northern shelf of Elephant Island. Along a similar west-east transect approximately 50 km off the shelf, the northward transport of shelf waters was approximately 2.4 and 1.2 Sv in the austral winter and summer, respectively. The waters around Elephant Island primarily consist of the UCDW that has been modified by local cooling and freshening, unmodified UCDW that has recently intruded onto the shelf, and Bransfield Current water that is a mixture of shelf and Bransfield Strait waters. Weddell Sea outflows were observed which affect the hydrography and circulation in the Bransfield Strait and indirectly affect the circulation patterns in the southern Drake Passage and around Elephant Island. Two Fe enrichment and transport mechanisms are proposed that intrusions of the UCDW onto the northern shelf region of the South Shetland Islands is considered as the results of Ekman pumping due to prevailing westerly wind in the region while the offshelf transport of shelf waters in the shelf region east of Elephant Island is due to acquisition of positive vorticity by shelf waters from horizontal mixing with onshelf intruded ACC waters.This project was supported by the National Science Foundation grant numbers OPP-0229966, ANT-0444040 and ANT-0948378 to M. Zhou, OPP0230445, ANT0443403 and ANT-0948357 to C. Measures, ANT0443869 and ANT-0948442 to M. Charette, and OPP0230443, ANT0444134 and ANT0948338 to B.G. Mitchell

Basin-scale inputs of cobalt, iron, and manganese from the Benguela-Angola front to the South Atlantic Ocean

Author Posting. © Association for the Sciences of Limnology and Oceanography, 2012. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography 57 (2012): 989-1010, doi:10.4319/lo.2012.57.4.0989.We present full-depth zonal sections of total dissolved cobalt, iron, manganese, and labile cobalt from the South Atlantic Ocean. A basin-scale plume from the African coast appeared to be a major source of dissolved metals to this region, with high cobalt concentrations in the oxygen minimum zone of the Angola Dome and extending 2500 km into the subtropical gyre. Metal concentrations were elevated along the coastal shelf, likely due to reductive dissolution and resuspension of particulate matter. Linear relationships between cobalt, N2O, and O2, as well as low surface aluminum supported a coastal rather than atmospheric cobalt source. Lateral advection coupled with upwelling, biological uptake, and remineralization delivered these metals to the basin, as evident in two zonal transects with distinct physical processes that exhibited different metal distributions. Scavenging rates within the coastal plume differed for the three metals; iron was removed fastest, manganese removal was 2.5 times slower, and cobalt scavenging could not be discerned from water mass mixing. Because scavenging, biological utilization, and export constantly deplete the oceanic inventories of these three hybrid-type metals, point sources of the scale observed here likely serve as vital drivers of their oceanic cycles. Manganese concentrations were elevated in surface waters across the basin, likely due to coupled redox processes acting to concentrate the dissolved species there. These observations of basin-scale hybrid metal plumes combined with the recent projections of expanding oxygen minimum zones suggest a potential mechanism for effects on ocean primary production and nitrogen fixation via increases in trace metal source inputs.This research was supported US National Science Foundation Chemical Oceanography (Division of Ocean Sciences OCE-0452883, OCE-0752291, OCE-0928414, OCE-1031271), the Center for Microbial Research and Education, the Gordon and Betty Moore Foundation, the WHOI Coastal Ocean Institute, and the WHOI Ocean Life Institute