A seasonal study of dissolved cobalt in the Ross Sea, Antarctica : micronutrient behavior, absence of scavenging, and relationships with Zn, Cd, and P

© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 7 (2010): 4059-4082, doi:10.5194/bg-7-4059-2010.We report the distribution of cobalt (Co) in the Ross Sea polynya during austral summer 2005–2006 and the following austral spring 2006. The vertical distribution of total dissolved Co (dCo) was similar to soluble reactive phosphate (PO43−), with dCo and PO43− showing a significant correlation throughout the water column (r2 = 0.87, 164 samples). A strong seasonal signal for dCo was observed, with most spring samples having concentrations ranging from ~45–85 pM, whereas summer dCo values were depleted below these levels by biological activity. Surface transect data from the summer cruise revealed concentrations at the low range of this seasonal variability (~30 pM dCo), with concentrations as low as 20 pM observed in some regions where PO43− was depleted to ~0.1 μM. Both complexed Co, defined as the fraction of dCo bound by strong organic ligands, and labile Co, defined as the fraction of dCo not bound by these ligands, were typically observed in significant concentrations throughout the water column. This contrasts the depletion of labile Co observed in the euphotic zone of other ocean regions, suggesting a much higher bioavailability for Co in the Ross Sea. An ecological stoichiometry of 37.6 μmol Co:mol−1 PO43− calculated from dissolved concentrations was similar to values observed in the subarctic Pacific, but approximately tenfold lower than values in the Eastern Tropical Pacific and Equatorial Atlantic. The ecological stoichiometries for dissolved Co and Zn suggest a greater overall use of Zn relative to Co in the shallow waters of the Ross Sea, with a Co:PO43−/Zn:PO43− ratio of 1:17. Comparison of these observed stoichiometries with values estimated in culture studies suggests that Zn is a key micronutrient that likely influences phytoplankton diversity in the Ross Sea. In contrast, the observed ecological stoichiometries for Co were below values necessary for the growth of eukaryotic phytoplankton in laboratory culture experiments conducted in the absence of added zinc, implying the need for significant Zn nutrition in the Zn-Co cambialistic enzymes. The lack of an obvious kink in the dissolved Co:PO43− relationship was in contrast to Zn:PO43− and Cd:PO43− kinks previously observed in the Ross Sea. An excess uptake mechanism for kink formation is proposed as a major driver of Cd:PO43− kinks, where Zn and Cd uptake in excess of that needed for optimal growth occurs at the base of the euphotic zone, and no clear Co kink occurs because its abundances are too low for excess uptake. An unusual characteristic of Co geochemistry in the Ross Sea is an apparent lack of Co scavenging processes, as inferred from the absence of dCo removal below the euphotic zone. We hypothesize that this vertical distribution reflects a low rate of Co scavenging by Mn oxidizing bacteria, perhaps due to Mn scarcity, relative to the timescale of the annual deep winter mixing in the Ross Sea. Thus Co exhibits nutrient-like behavior in the Ross Sea, in contrast to its hybrid-type behavior in other ocean regions, with implications for the possibility of increased marine Co inventories and utility as a paleooceanographic proxy.This research was supported by the US National Science Foundation through research grants (OPP-0440840, OPP-0338097, OPP-0732665, OCE-0452883, OCE-0752991, OCE-0928414)

Thaumarchaeal ecotype distributions across the equatorial Pacific Ocean and their potential roles in nitrification and sinking flux attenuation

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Limnology and Oceanography 62 (2017): 1984–2003, doi:10.1002/lno.10547.Thaumarchaea are among the most abundant microbial groups in the ocean, but controls on their abundance and the distribution and metabolic potential of different subpopulations are poorly constrained. Here, two ecotypes of ammonia-oxidizing thaumarchaea were quantified using ammonia monooxygenase (amoA) genes across the equatorial Pacific Ocean. The shallow, or water column “A” (WCA), ecotype was the most abundant ecotype at the depths of maximum nitrification rates, and its abundance correlated with other biogeochemical indicators of remineralization such as NO3 : Si and total Hg. Metagenomes contained thaumarchaeal genes encoding for the catalytic subunit of the urease enzyme (ureC) at all depths, suggesting that members of both WCA and the deep, water column “B” (WCB) ecotypes may contain ureC. Coupled urea hydrolysis-ammonia oxidation rates were similar to ammonia oxidation rates alone, suggesting that urea could be an important source of ammonia for mesopelagic ammonia oxidizers. Potential inducement of metal limitation of both ammonia oxidation and urea hydrolysis was demonstrated via additions of a strong metal chelator. The water column inventory of WCA was correlated with the depth-integrated abundance of WCB, with both likely controlled by the flux of sinking particulate organic matter, providing strong evidence of vertical connectivity between the ecotypes. Further, depth-integrated amoA gene abundance and nitrification rates were correlated with particulate organic nitrogen flux measured by contemporaneously deployed sediment traps. Together, the results refine our understanding of the controls on thaumarchaeal distributions in the ocean, and provide new insights on the relationship between material flux and microbial communities in the mesopelagic.United States National Science Foundation (NSF) Grant Numbers: OCE-1260006, OCE-1031271, OCE-1337780, OCE-1259994; University of Maryland Center for Environmental Science (UMCES); JGI Community Sequencing Project 133

Constraints on the northwestern Atlantic deep water circulation from 231 Pa/ 230 Th during the last 30,000 years

Global climatic changes during the last Glacial and Deglacial have been related to variations of the Atlantic Meridional Overturning Circulation (AMOC). Here, we present new and refined 231Pa/230Th down‐core profiles extending back to 30 ka BP from the northwestern Atlantic along the Atlantic Deep Western Boundary Current (DWBC), which is the main component of the southward deep backflow of the AMOC. Besides the well‐known Bermuda Rise records, available high‐resolution 231Pa/230Th data in the northwestern Atlantic are still sparse. Our new records along with reconstructions of deep water provenance from Nd isotopes constrain the timing and magnitude of past changes in AMOC from an additional northwestern Atlantic region forming a depth transect between 3000 and 4760 m water depth. Our extended and improved dataset confirms the weakening of the AMOC during deglacial cold spells such as Heinrich Event 1 and the Younger Dryas interrupted by a reinvigoration during the Bølling‐Allerød interstadial as seen in the prominent 231Pa/230Th records from the Bermuda Rise. However, in contrast to the Bermuda Rise records we find a clearly reduced circulation strength during the Last Glacial Maximum in the deep Atlantic

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

The Arabian Sea as a high-nutrient, low-chlorophyll region during the late Southwest Monsoon

© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 7 (2010): 2091-2100, doi:10.5194/bg-7-2091-2010.Extensive observations were made during the late Southwest Monsoon of 2004 over the Indian and Omani shelves, and along a transect that extended from the southern coast of Oman to the central west coast of India, tracking the southern leg of the US JGOFS expedition (1994–1995) in the west. The data are used, in conjunction with satellite-derived data, to investigate long-term trends in chlorophyll and sea surface temperature, indicators of upwelling intensity, and to understand factors that control primary production (PP) in the Arabian Sea, focussing on the role of iron. Our results do not support an intensification of upwelling in the western Arabian Sea, reported to have been caused by the decline in the winter/spring Eurasian snow cover since 1997. We also noticed, for the first time, an unexpected development of high-nutrient, low-chlorophyll condition off the southern Omani coast. This feature, coupled with other characteristics of the system, such as a narrow shelf and relatively low iron concentrations in surface waters, suggest a close similarity between the Omani upwelling system and the Peruvian and California upwelling systems, where PP is limited by iron. Iron limitation of PP may complicate simple relationship between upwelling and PP assumed by previous workers, and contribute to the anomalous offshore occurrence of the most severe oxygen (O2) depletion in the region. Over the much wider Indian shelf, which experiences large-scale bottom water O2-depletion in summer, adequate iron supply from reducing bottom-waters and sediments seems to support moderately high PP; however, such production is restricted to the thin, oxygenated surface layer, probably because of the unsuitability of the O2-depleted environment for the growth of oxygenic photosynthesizers.Financial support was provided by CSIR through the Network Project CMM0009 to SWAN and by NSF through OCE-0327227S to JWM

Minimal cobalt metabolism in the marine cyanobacterium Prochlorococcus.

Despite very low concentrations of cobalt in marine waters, cyanobacteria in the genus Prochlorococcus retain the genetic machinery for the synthesis and use of cobalt-bearing cofactors (cobalamins) in their genomes. We explore cobalt metabolism in a Prochlorococcus isolate from the equatorial Pacific Ocean (strain MIT9215) through a series of growth experiments under iron- and cobalt-limiting conditions. Metal uptake rates, quantitative proteomic measurements of cobalamin-dependent enzymes, and theoretical calculations all indicate that Prochlorococcus MIT9215 can sustain growth with less than 50 cobalt atoms per cell, ∼100-fold lower than minimum iron requirements for these cells (∼5,100 atoms per cell). Quantitative descriptions of Prochlorococcus cobalt limitation are used to interpret the cobalt distribution in the equatorial Pacific Ocean, where surface concentrations are among the lowest measured globally but Prochlorococcus biomass is high. A low minimum cobalt quota ensures that other nutrients, notably iron, will be exhausted before cobalt can be fully depleted, helping to explain the persistence of cobalt-dependent metabolism in marine cyanobacteria

Living on the edge: environmental variability of a shallow late Holocene cold-water coral mound

Similar to their tropical counterparts, cold-water corals (CWCs) are able to build large three-dimensional reef structures. These unique ecosystems are at risk due to ongoing climate change. In particular, ocean warming, ocean acidification and changes in the hydrological cycle may jeopardize the existence of CWCs. In order to predict how CWCs and their reefs or mounds will develop in the near future one important strategy is to study past fossil CWC mounds and especially shallow CWC ecosystems as they experience a greater environmental variability compared to other deep-water CWC ecosystems. We present results from a CWC mound off southern Norway. A sediment core drilled from this relatively shallow (~ 100 m) CWC mound exposes in full detail hydrographical changes during the late Holocene, which were crucial for mound build-up. We applied computed tomography, 230Th/U dating, and foraminiferal geochemical proxy reconstructions of bottom-water-temperature (Mg/Ca-based BWT), δ18O for seawater density, and the combination of both to infer salinity changes. Our results demonstrate that the CWC mound formed in the late Holocene between 4 kiloannum (ka) and 1.5 ka with an average aggradation rate of 104 cm/kiloyears (kyr), which is significantly lower than other Holocene Norwegian mounds. The reconstructed BWTMg/Ca and seawater density exhibit large variations throughout the entire period of mound formation, but are strikingly similar to modern in situ observations in the nearby Tisler Reef. We argue that BWT does not exert a primary control on CWC mound formation. Instead, strong salinity and seawater density variation throughout the entire mound sequence appears to be controlled by the interplay between the Atlantic Water (AW) inflow and the overlying, outflowing Baltic-Sea water. CWC growth and mound formation in the NE Skagerrak was supported by strong current flow, oxygen replenishment, the presence of a strong boundary layer and larval dispersal through the AW, but possibly inhibited by the influence of fresh Baltic Water during the late Holocene. Our study therefore highlights that modern shallow Norwegian CWC reefs may be particularly endangered due to changes in water-column stratification associated with increasing net precipitation caused by climate change

Human Non-neutralizing HIV-1 Envelope Monoclonal Antibodies Limit the Number of Founder Viruses during SHIV Mucosal Infection in Rhesus Macaques

HIV-1 mucosal transmission begins with virus or virus-infected cells moving through mucus across mucosal epithelium to infect CD4+ T cells. Although broadly neutralizing antibodies (bnAbs) are the type of HIV-1 antibodies that are most likely protective, they are not induced with current vaccine candidates. In contrast, antibodies that do not neutralize primary HIV-1 strains in the TZM-bl infection assay are readily induced by current vaccine candidates and have also been implicated as secondary correlates of decreased HIV-1 risk in the RV144 vaccine efficacy trial. Here, we have studied the capacity of anti-Env monoclonal antibodies (mAbs) against either the immunodominant region of gp41 (7B2 IgG1), the first constant region of gp120 (A32 IgG1), or the third variable loop (V3) of gp120 (CH22 IgG1) to modulate in vivo rectal mucosal transmission of a high-dose simian-human immunodeficiency virus (SHIV-BaL) in rhesus macaques. 7B2 IgG1 or A32 IgG1, each containing mutations to enhance Fc function, was administered passively to rhesus macaques but afforded no protection against productive clinical infection while the positive control antibody CH22 IgG1 prevented infection in 4 of 6 animals. Enumeration of transmitted/founder (T/F) viruses revealed that passive infusion of each of the three antibodies significantly reduced the number of T/F genomes. Thus, some antibodies that bind HIV-1 Env but fail to neutralize virus in traditional neutralization assays may limit the number of T/F viruses involved in transmission without leading to enhancement of viral infection. For one of these mAbs, gp41 mAb 7B2, we provide the first co-crystal structure in complex with a common cyclical loop motif demonstrated to be critical for infection by other retroviruses

Reduced iron associated with secondary nitrite maxima in the Arabian Sea

Dissolved iron and Fe(II) were measured in the oxygen minimum zone (OMZ) of the Arabian Sea in September 2004. The OMZ is a well-demarcated feature characterized by high rates of denitrification, and a deep nitrite maximum coinciding with oxygen levels below 1 μmol L-1. This zone is significantly enriched in dissolved Fe relative to overlying and underlying waters and up to 50% of the dissolved Fe is present as Fe(II). The maxima in Fe(II) are at the same depth as the deep nitrite maxima, centered around 200-250 m. They coincide with a local maximum in total dissolved Fe, suggesting that Fe accumulates at this depth because of the greater solubility of Fe(II) over Fe(III). Fe(II) is thermodynamically unstable even at submicromolar oxygen levels, so active biological reduction is the most plausible source. To our knowledge, this is the first report of a potential link between Fe reduction, elevated dissolved Fe concentrations, and nitrite accumulation within an OMZ. Denitrification has a high Fe requirement associated with the metalloenzymes for nitrate and nitrite reduction, so in situ redox cycling of Fe has important implications for the nitrogen cycle