A nutrient limitation mosaic in the eastern tropical Indian Ocean

The Indian Ocean accounts for about one fifth of global ocean net primary production but remains undersampled relative to other major ocean basins. The eastern tropical Indian Ocean is characterized by extremely low concentrations of both macronutrients and the micronutrient iron. We measured concentrations of dissolved and particulate trace metals (Fe, Mn, Zn, Pb) in the upper ocean along the GO-SHIP IO9N transect (28˚S to 17˚N, mostly along the 95˚E meridian) during a cruise in April 2016. Cellular quotas (metal/C) of Fe, Mn, Co, Ni, Cu, and Zn were measured in small eukaryotic flagellates (2–7 μm). Deckboard bottle incubation experiments were conducted at one station in each of three putative biogeochemical regions: southern Indian Ocean gyre (SIO, 28-10˚S); equatorial Indian Ocean (EqIO, 10˚S - 5˚N); Bay of Bengal (BoB, 5-17˚N). Nitrate and phosphate were below detection limits in surface waters across the transect. Dissolved and particulate Fe were <0.2 nM south of 10˚N and lowest in the EqIO. Cellular Fe/C quotas were approximately 6 μmoL/mol and did not vary along the transect, nor did cellular Mn/C or Co/C quotas. Cellular Ni/C and Zn/C quotas were significantly higher at the southern terminus. Nutrient addition experiments indicated that N was the primary limiting nutrient for autotrophs using chlorophyll a as a proxy, but biomass measurements of specific phytoplankton groups pointed to a more complex nutrient limitation mosaic. Prochlorococcus was limited by N in the EqIO but by multiple nutrients (N, P, and/or Fe) in the BoB. Synechococcus was limited by N in the EqIO and BoB, while small (<20 μm) eukaryotic phytoplankton were limited by N in the EqIO and by multiple nutrients in the BoB. Stoichiometric comparisons of cells and underlying source waters indicate a gradient of N and Fe stress along the transect. These data demonstrate that autotroph communities are poised near multiple nutrient limitation horizons in extremely oligotrophic waters far from micronutrient sources

Comparison of particulate trace element concentrations in the North Atlantic Ocean as determined with discrete bottle sampling and in situ pumping

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): 272-282, doi:10.1016/j.dsr2.2014.11.005.The oceanic geochemical cycles of many metals are controlled, at least in part, by interactions with particulate matter, and measurements of particulate trace metals are a core component of the international GEOTRACES program. Particles can be collected by several methods, including in-line filtration from sample bottles and in situ pumping. Both approaches were used to collect particles from the water column on the U.S. GEOTRACES North Atlantic Zonal Transect cruises. Statistical comparison of 91 paired samples collected at matching stations and depths indicate mean concentrations within 5% for Fe and Ti, within 10% for Cd, Mn and Co, and within 15% for Al. Particulate concentrations were higher in bottle samples for Cd, Mn and Co but lower in bottle samples for Fe, Al and Ti, suggesting that large lithogenic particles may be undersampled by bottles in near-shelf environments. In contrast, P was 58% higher on average in bottle samples. This is likely due to a combination of analytical offsets between lab groups, differences in filter pore size, and potential loss of labile P from pump samples following misting with deionized water. Comparable depth profiles were produced by the methods across a range of conditions in the North Atlantic.This work was funded by grants from the US National Science Foundation to BST (OCE-0928289) and PJL (OCE-0963026) as part of the US GEOTRACES North Atlantic Zonal Transect program

Elevated Trace Metal Content of Prokaryotic Communities Associated with Marine Oxygen Deficient Zones

Little is known about the trace metal content of marine prokaryotes, in part due to their co-occurrence with more abundant particulate phases in the upper ocean, such as phytoplankton and biogenic detritus, lithogenic minerals, and authigenic Mn and Fe oxyhydroxides. We attempt to isolate these biomass signals in particulate data from the US GEOTRACES Eastern Pacific Zonal Transect (cruise GP16) in the Eastern Tropical South Pacific (ETSP), which exhibited consistent maxima in P and other bioactive trace metals, and minima in particulate Mn, in the oxygen deficient zones (ODZs) of 13 stations. Nitrite maxima and nitrate deficits indicated the presence of denitrifying prokaryotic biomass within ETSP ODZs, and deep secondary fluorescence maxima at the upper ODZ boundaries of 10 stations also suggested the presence of low-light, autotrophic communities. ODZs were observed as far west as 99 degrees W, more than 2300 km from the South American coast, where eolian lithogenic and lateral/resuspended sedimentary inputs were negligible, presenting a unique opportunity to examine prokaryotic metal stoichiometries. ODZ particulate P maxima can rival gyre mixed layer biomass concentrations, are highly sensitive to oxygen, and are in excess of amounts scavengable by local Fe oxyhydroxides and acid-volatile sulfides. Even after correction for lithogenic and ferruginous-scavenged metals, ODZ P-maxima are often enriched in Cd, Co, Cu, Ni, V, and Zn, exhibiting particulate trace metal ratios to P that exceed mixed layer biomass ratios by factors of 2-9. ODZ prokaryotic communities may be largely hidden, TM-rich pools involved in the marine cycles of these bioactive trace metals

Popular attitudes to memory, the body, and social identity : the rise of external commemoration in Britain, Ireland, and New England

A comparative analysis of samples of external memorials from burial grounds in Britain, Ireland and New England reveals a widespread pattern of change in monument style and content, and exponential growth in the number of permanent memorials from the 18th century onwards. Although manifested in regionally distinctive styles on which most academic attention has so far been directed, the expansion reflects global changes in social relationships and concepts of memory and the body. An archaeological perspective reveals the importance of external memorials in articulating these changing attitudes in a world of increasing material consumption

Authigenic Iron Is a Significant Component of Oceanic Labile Particulate Iron Inventories

Particulate phases transport trace metals (TM) and thereby exert a major control on TM distribution in the ocean. Particulate TMs can be classified by their origin as lithogenic (crustal material), biogenic (cellular), or authigenic (formed in situ), but distinguishing these fractions analytically in field samples is a challenge often addressed using operational definitions and assumptions. These different phases require accurate characterization because they have distinct roles in the biogeochemical iron cycle. Particles collected from the upper 2,000 m of the northwest subtropical Atlantic Ocean over four seasonal cruises throughout 2019 were digested with a chemical leach to operationally distinguish labile particulate material from refractory lithogenics. Direct measurements of cellular iron (Fe) were used to calculate the biogenic contribution to the labile Fe fraction, and any remaining labile material was defined as authigenic. Total particulate Fe (PFe) inventories varied \u3c15% between seasons despite strong seasonality in dust inputs. Across seasons, the total PFe inventory (±1SD) was composed of 73 ± 13% lithogenic, 18 ± 7% authigenic, and 10 ± 8% biogenic Fe above the deep chlorophyll maximum (DCM), and 69 ± 8% lithogenic, 30 ± 8% authigenic, and 1.1 ± 0.5% biogenic Fe below the DCM. Data from three other ocean regions further reveal the importance of the authigenic fraction across broad productivity and Fe gradients, comprising ca. 20%-27% of total PFe

Iron storage capacities and associated ferritin gene expression among marine diatoms

In large regions of the ocean, low iron availability regulates diatom growth and species composition. Diatom species often vary in their physiological response to iron enrichment, with natural and artificial iron additions in iron-limited regions of the ocean resulting in large blooms of primarily pennate diatoms. The ability of pennate diatoms to proliferate following pulse iron additions has been partly attributed to their ability to acquire and store excess intracellular iron in the iron storage protein ferritin. Recent transcriptome sequencing of diatoms indicate that some centric diatoms also possess ferritin. Using a combination of physiological and molecular techniques, we examined the iron storage capacities and associated ferritin gene expression in phylogenetically diverse centric and pennate diatoms grown under high and low iron concentrations. There were no systematic differences among ferritin-containing and non-containing diatom lineages in their ability to store iron in excess of that needed to support maximum growth rates. An exception, however, was the ferritin-containing pennate diatom Pseudo-nitzschia granii, native to iron-limited waters of the Northeast Pacific Ocean. This species exhibited an exceptionally large luxury iron storage capacity and increased ferritin gene expression at high iron concentrations, supporting a role in long-term iron storage. By contrast, two other diatoms species that exhibited minimal iron storage capacities contained two distinct ferritin genes where one ferritin gene increased in expression under iron limitation while the second showed no variation with cellular iron status. We conclude that ferritin may serve multiple functional roles that are independent of diatom phylogeny

Taxonomic and nutrient controls on phytoplankton iron quotas in the ocean

Phytoplankton iron contents (i.e., quotas) directly link biogeochemical cycles of iron and carbon and drive patterns of nutrient limitation, recycling, and export. Ocean biogeochemical models typically assume that iron quotas are either static or controlled by dissolved iron availability. We measured iron quotas in phytoplankton communities across nutrient gradients in the Pacific Ocean and found that quotas diverged significantly in taxon-specific ways from laboratory-derived predictions. Iron quotas varied 40-fold across nutrient gradients, and nitrogen-limitation allowed diatoms to accumulate fivefold more iron than co-occurring flagellates even under low iron availability. Modeling indicates such “luxury” uptake is common in large regions of the low-iron Pacific Ocean. Among diatoms, both pennate and centric genera accumulated luxury iron, but the cosmopolitan pennate genus Pseudo-nitzschia maintained iron quotas 10-fold higher than co-occurring centric diatoms, likely due to enhanced iron storage. Biogeochemical models should account for taxonomic and macronutrient controls on phytoplankton iron quotas

The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt

The Great Calcite Belt (GCB) of the Southern Ocean is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region, provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. Water samples for phytoplankton enumeration were collected from the upper 30 m during two cruises, the first to the South Atlantic sector (Jan–Feb 2011; 60 °W–15 °E and 36–60 °S) and the second in the South Indian sector (Feb–Mar 2012; 40–120 °E and 36–60 °S). The species composition of coccolithophores and diatoms was examined using scanning electron microscopy at 27 stations across the Sub-Tropical, Polar, and Sub-Antarctic Fronts. The influence of environmental parameters, such as sea-surface temperature (SST), salinity, carbonate chemistry (i.e., pH, partial pressure of CO2 (pCO2), alkalinity, dissolved inorganic carbon), macro-nutrients (i.e., nitrate + nitrite, phosphate, silicic acid, ammonia), and mixed layer average irradiance, on species composition across the GCB, was assessed statistically. Nanophytoplankton (cells 2–20 μm) were the numerically abundant size group of biomineralizing phytoplankton across the GCB, the coccolithophore Emiliania huxleyi and the diatoms Fragilariopsis nana, F. pseudonana and Pseudonitzschia sp. were the most dominant and widely distributed species. A combination of SST, macro-nutrient concentrations and pCO2 were the best statistical descriptors of biogeographic variability of biomineralizing species composition between stations. Emiliania huxleyi occurred in the silicic acid-depleted waters between the Sub-Antarctic Front and the Polar Front, indicating a favorable environment for this coccolithophore in the GCB after spring diatom blooms remove silicic acid to limiting levels. After full consideration of variability in carbonate chemistry and temperature on the distribution of nanoplankton in the GCB, we find that temperature remains the dominant driver of biogeography in a large proportion of the modern Southern Ocean

The Arctic Summer Cloud Ocean Study (ASCOS): overview and experimental design

The climate in the Arctic is changing faster than anywhere else on earth. Poorly understood feedback processes relating to Arctic clouds and aerosol-cloud interactions contribute to a poor understanding of the present changes in the Arctic climate system, and also to a large spread in projections of future climate in the Arctic. The problem is exacerbated by the paucity of research-quality observations in the central Arctic. Improved formulations in climate models require such observations, which can only come from measurements in situ in this difficult-to-reach region with logistically demanding environmental conditions. The Arctic Summer Cloud Ocean Study (ASCOS) was the most extensive central Arctic Ocean expedition with an atmospheric focus during the International Polar Year (IPY) 2007-2008. ASCOS focused on the study of the formation and life cycle of low-level Arctic clouds. ASCOS departed from Longyearbyen on Svalbard on 2 August and returned on 9 September 2008. In transit into and out of the pack ice, four short research stations were undertaken in the Fram Strait: two in open water and two in the marginal ice zone. After traversing the pack ice northward, an ice camp was set up on 12 August at 87°21′ N, 01°29′ W and remained in operation through 1 September, drifting with the ice. During this time, extensive measurements were taken of atmospheric gas and particle chemistry and physics, mesoscale and boundary-layer meteorology, marine biology and chemistry, and upper ocean physics. ASCOS provides a unique interdisciplinary data set for development and testing of new hypotheses on cloud processes, their interactions with the sea ice and ocean and associated physical, chemical, and biological processes and interactions. For example, the first-ever quantitative observation of bubbles in Arctic leads, combined with the unique discovery of marine organic material, polymer gels with an origin in the ocean, inside cloud droplets suggests the possibility of primary marine organically derived cloud condensation nuclei in Arctic stratocumulus clouds. Direct observations of surface fluxes of aerosols could, however, not explain observed variability in aerosol concentrations, and the balance between local and remote aerosols sources remains open. Lack of cloud condensation nuclei (CCN) was at times a controlling factor in low-level cloud formation, and hence for the impact of clouds on the surface energy budget. ASCOS provided detailed measurements of the surface energy balance from late summer melt into the initial autumn freeze-up, and documented the effects of clouds and storms on the surface energy balance during this transition. In addition to such process-level studies, the unique, independent ASCOS data set can and is being used for validation of satellite retrievals, operational models, and reanalysis data sets