Sedwick Peter N.

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Sedwick

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Peter N.

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Temporal progression of photosynthetic-strategy in phytoplankton in the Ross Sea, Antarctica

( 2015-12) Ryan-Keogh, Thomas J. ; DeLizo, Liza M. ; Smith, Walker O. ; Sedwick, Peter N. ; McGillicuddy, Dennis J. ; Moore, C. Mark ; Bibby, Thomas S.

The bioavailability of iron influences the distribution, biomass and productivity of phytoplankton in the Ross Sea, one of the most productive regions in the Southern Ocean. We mapped the spatial and temporal extent and severity of iron-limitation of the native phytoplankton assemblage using long- (>24 h) and short-term (24 h) iron- addition experiments along with physiological and molecular characterisations during a cruise to the Ross Sea in December-February 2012. Phytoplankton increased their photosynthetic efficiency in response to iron addition, suggesting proximal iron limitation throughout most of the Ross Sea during summer. Molecular and physiological data further indicate that as nitrate is removed from the surface ocean the phytoplankton community transitions to one displaying an iron-efficient photosynthetic strategy characterised by an increase in the size of photosystem II (PSII) photochemical cross section (σPSII) and a decrease in the chlorophyll-normalised PSII abundance. These results suggest that phytoplankton with the ability to reduce their photosynthetic iron requirements are selected as the growing season progresses, which may drive the well-documented progression from Phaeocystis antarctica- assemblages to diatom-dominated phytoplankton. Such a shift in the assemblage-level photosynthetic strategy potentially mediates further drawdown of nitrate following the development of iron deficient conditions in the Ross Sea.
Distributions, sources, and transformations of dissolved and particulate iron on the Ross Sea continental shelf during summer

(John Wiley & Sons, 2017-08-17) Marsay, Christopher M. ; Barrett, Pamela M. ; McGillicuddy, Dennis J. ; Sedwick, Peter N.

We report water column dissolved iron (dFe) and particulate iron (pFe) concentrations from 50 stations sampled across the Ross Sea during austral summer (January–February) of 2012. Concentrations of dFe and pFe were measured in each of the major Ross Sea water masses, including the Ice Shelf Water and off-shelf Circumpolar Deep Water. Despite significant lateral variations in hydrography, macronutrient depletion, and primary productivity across several different regions on the continental shelf, dFe concentrations were consistently low (<0.1 nM) in surface waters, with only a handful of stations showing elevated concentrations (0.20–0.45 nM) in areas of melting sea ice and near the Franklin Island platform. Across the study region, pFe associated with suspended biogenic material approximately doubled the inventory of bioavailable iron in surface waters. Our data reveal that the majority of the summertime iron inventory in the Ross Sea resides in dense shelf waters, with highest concentrations within 50 m of the seafloor. Higher dFe concentrations near the seafloor are accompanied by an increased contribution to pFe from authigenic and/or scavenged iron. Particulate manganese is also influenced by sediment resuspension near the seafloor but, unlike pFe, is increasingly associated with authigenic material higher in the water column. Together, these results suggest that following depletion of the dFe derived from wintertime convective mixing and sea ice melt, recycling of pFe in the upper water column plays an important role in sustaining the summertime phytoplankton bloom in the Ross Sea polynya.
Iron limitation of a springtime bacterial and phytoplankton community in the Ross Sea : implications for vitamin B12 nutrition

(Frontiers Media, 2011-08-15) Bertrand, Erin M. ; Saito, Mak A. ; Lee, Peter A. ; Dunbar, Robert B. ; Sedwick, Peter N. ; DiTullio, Giacomo R.

The Ross Sea is home to some of the largest phytoplankton blooms in the Southern Ocean. Primary production in this system has previously been shown to be iron limited in the summer and periodically iron and vitamin B12 colimited. In this study, we examined trace metal limitation of biological activity in the Ross Sea in the austral spring and considered possible implications for vitamin B12 nutrition. Bottle incubation experiments demonstrated that iron limited phytoplankton growth in the austral spring while B12, cobalt, and zinc did not. This is the first demonstration of iron limitation in a Phaeocystis antarctica-dominated, early season Ross Sea phytoplankton community. The lack of B12 limitation in this location is consistent with previous Ross Sea studies in the austral summer, wherein vitamin additions did not stimulate P. antarctica growth and B12 was limiting only when bacterial abundance was low. Bottle incubation experiments and a bacterial regrowth experiment also revealed that iron addition directly enhanced bacterial growth. B12 uptake measurements in natural water samples and in an iron fertilized bottle incubation demonstrated that bacteria serve not only as a source for vitamin B12, but also as a significant sink, and that iron additions enhanced B12 uptake rates in phytoplankton but not bacteria. Additionally, vitamin uptake rates did not become saturated upon the addition of up to 95 pM B12. A rapid B12 uptake rate was observed after 13 min, which then decreased to a slower constant uptake rate over the next 52 h. Results from this study highlight the importance of iron availability in limiting early season Ross Sea phytoplankton growth and suggest that rates of vitamin B12 production and consumption may be impacted by iron availability.
On the fractional solubility of copper in marine aerosols : toxicity of aeolian copper revisited

(American Geophysical Union, 2010-10-19) Sholkovitz, Edward R. ; Sedwick, Peter N. ; Church, Thomas M.

Paytan et al. (2009) argue that the atmospheric deposition of aerosols lead to copper concentrations that are potentially toxic to marine phytoplankton in a large area of tropical and subtropical North Atlantic Ocean. A key assumption in their model is that all marine aerosols (mineral dust and anthropogenic particles) have a high (40%) fractional solubility of copper. Our data show that the fractional solubility of copper for Saharan dust over the Sargasso Sea and Bermuda is significantly lower (1–7%). In contrast, anthropogenic aerosols with non-Saharan sources have significantly higher values (10–100%). Hence, the potential Cu toxicity in the tropical and subtropical North Atlantic should be re-estimated, given the low fractional solubility of Cu in the Saharan dust that dominates aerosol deposition to this region.
Concentrations of dissolved aluminum (Al) in samples collected during the U.S. GEOTRACES EPZT cruise (R/V Thomas G. Thompson TN303) from October to December 2013

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-07-31) Resing, Joseph A. ; Sedwick, Peter N.

Concentrations of dissolved aluminum in samples collected on the U.S. GEOTRACES EPZT cruise. These Al data were collected as a part of the US GEOTRACES EPZT cruise and were initially reported by Resing et al., (2015). Those data were analyzed and processed at sea. The data reported here have been corrected, based on reevaluating peak processing, drift corrections, and through the removal of errant data points. Additional missing data points have been also been added. Those data points are mostly from the Fish surface ocean sampler. These revised data are reported in Ho et al. (2019). 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/819735
Concentrations of dissolved iron and dissolved iron(II) from R/V Knorr cruises KN199-04 and KN204-01 in the Subtropical northern Atlantic Ocean from 2010-2011 (U.S. GEOTRACES NAT project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2021-05-12) Sedwick, Peter N. ; Bowie, Andrew R.

This dataset includes concentrations of dissolved iron and dissolved iron(II) from R/V Knorr cruises KN199-04 and KN204-01 in the Subtropical northern Atlantic Ocean from 2010-2011 (U.S. GEOTRACES NAT 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/3826
Trace metals, hydrography, and fluorescence from CTD casts on the RVIB Nathaniel B. Palmer (cruise NBP1704) in the Ross Sea, Antarctica from April to May 2017

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2021-09-08) Sedwick, Peter N.

Water column samples for analysis of trace elements (dissolved, soluble, and particulate), and continuous profiles of temperature, salinity, chlorophyll fluorescence, and dissolved oxygen concentration were collected from CTD casts on the RVIB Nathaniel B. Palmer (cruise NBP1704) in the Ross Sea, Antarctica from April to May 2017. 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/856009
Trace-metals from CTD casts and underway water samples collected during the R/V Hugh R. Sharp cruise HRS1414 in the Mid and South-Atlantic Bight in August of 2014 (DANCE project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-08-15) Sedwick, Peter N. ; Mulholland, Margaret ; Najjar, Raymond

Dissolved iron, nitrate+nitrite, ammonium, and phosphate were measured from CTD bottle samples, and underway water samples collected with a towfish system during the R/V Hugh R. Sharp cruise HRS1414 in the Mid and South-Atlantic Bight in August of 2014. This dataset also includes temperature, salinity, chlorophyll fluorescence, depth, latitude, and longitude. 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/734324
Nutrients and iron in shipboard aerosol and rain samples collected during R/V Hugh R. Sharp cruise HRS1414 in the Mid-Atlantic Bight and northern South-Atlantic Bight from July to August of 2014 (DANCE project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-08-15) Sedwick, Peter N. ; Mulholland, Margaret ; Najjar, Raymond

Shipboard aerosol and rain samples were collected during R/V Hugh R. Sharp cruise HRS1414 offshore in the Mid-Atlantic Bight and northern South-Atlantic Bight from July to August of 2014. Samples were analyzed for nutrients and iron. 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/738744
A seasonal study of dissolved cobalt in the Ross Sea, Antarctica : micronutrient behavior, absence of scavenging, and relationships with Zn, Cd, and P

(Copernicus Publications on behalf of the European Geosciences Union, 2010-12-22) Saito, Mak A. ; Goepfert, Tyler J. ; Noble, Abigail E. ; Bertrand, Erin M. ; Sedwick, Peter N. ; DiTullio, Giacomo R.

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.
Dissolved inorganic nitrogen, chlorophyll-a, and primary production from bioassay experiments during the R/V Hugh R. Sharp cruise HRS1414 in the Mid and South-Atlantic Bight in August of 2014 (DANCE project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-08-15) Sedwick, Peter N. ; Mulholland, Margaret ; Najjar, Raymond

Three bioassay experiments were conducted in August of 2014 during the R/V Hugh R. Sharp cruise HRS1414 which generated measurements of dissolved inorganic nitrogen, chlorophyll-a and primary productivity. Treatments included various nutrient (N,Fe,P) additions and rainwater. This dataset was utilized in the following publication: Sedwick. P. N., et al. "Assessing phytoplankton nutritional status and potential impact of wet deposition in seasonally oligotrophic waters of the Mid-Atlantic Bight." Geophysical Research Letters (2018): doi: 10.1002/2017GL075361 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/734364
Early season depletion of dissolved iron in the Ross Sea polynya : implications for iron dynamics on the Antarctic continental shelf

(American Geophysical Union, 2011-12-15) Sedwick, Peter N. ; Marsay, Christopher M. ; Sohst, Bettina M. ; Aguilar-Islas, Ana M. ; Lohan, Maeve C. ; Long, Matthew C. ; Arrigo, Kevin R. ; Dunbar, Robert B. ; Saito, Mak A. ; Smith, Walker O. ; DiTullio, Giacomo R.

The Ross Sea polynya is among the most productive regions in the Southern Ocean and may constitute a significant oceanic CO2 sink. Based on results from several field studies, this region has been considered seasonally iron limited, whereby a “winter reserve” of dissolved iron (dFe) is progressively depleted during the growing season to low concentrations (~0.1 nM) that limit phytoplankton growth in the austral summer (December–February). Here we report new iron data for the Ross Sea polynya during austral summer 2005–2006 (27 December–22 January) and the following austral spring 2006 (16 November–3 December). The summer 2005–2006 data show generally low dFe concentrations in polynya surface waters (0.10 ± 0.05 nM in upper 40 m, n = 175), consistent with previous observations. Surprisingly, our spring 2006 data reveal similar low surface dFe concentrations in the polynya (0.06 ± 0.04 nM in upper 40 m, n = 69), in association with relatively high rates of primary production (~170–260 mmol C m−2 d−1). These results indicate that the winter reserve dFe may be consumed relatively early in the growing season, such that polynya surface waters can become “iron limited” as early as November; i.e., the seasonal depletion of dFe is not necessarily gradual. Satellite observations reveal significant biomass accumulation in the polynya during summer 2006–2007, implying significant sources of “new” dFe to surface waters during this period. Possible sources of this new dFe include episodic vertical exchange, lateral advection, aerosol input, and reductive dissolution of particulate iron.
Estimating the benthic efflux of dissolved iron on the Ross Sea continental shelf

(John Wiley & Sons, 2014-11-03) Marsay, Christopher M. ; Sedwick, Peter N. ; Dinniman, M. S. ; Barrett, Pamela M. ; Mack, Stefanie L. ; McGillicuddy, Dennis J.

Continental margin sediments provide a potentially large but poorly constrained source of dissolved iron (dFe) to the upper ocean. The Ross Sea continental shelf is one region where this benthic supply is thought to play a key role in regulating the magnitude of seasonal primary production. Here we present data collected during austral summer 2012 that reveal contrasting low surface (0.08 ± 0.07 nM) and elevated near-seafloor (0.74 ± 0.47 nM) dFe concentrations. Combining these observations with results from a high-resolution physical circulation model, we estimate dFe efflux of 5.8 × 107 mol yr−1 from the deeper portions (>400 m) of the Ross Sea continental shelf; more than sufficient to account for the inferred “winter reserve” dFe inventory at the onset of the growing season. In addition, elevated dFe concentrations observed over shallower bathymetry suggest that such features provide additional inputs of dFe to the euphotic zone throughout the year.
Fractional solubility of aerosol iron : synthesis of a global-scale data set

( 2012-04-06) Sholkovitz, Edward R. ; Sedwick, Peter N. ; Church, Thomas M. ; Baker, Alexander R. ; Powell, Claire F.

Aerosol deposition provides a major input of the essential micronutrient iron to the open ocean. A critical parameter with respect to biological availability is the proportion of aerosol iron that enters the oceanic dissolved iron pool – the so-called fractional solubility of aerosol iron (%FeS). Here we present a global-scale compilation of total aerosol iron loading (FeT) and estimated %FeS values for ~1100 samples collected over the open ocean, the coastal ocean, and some continental sites, including a new data set from the Atlantic Ocean. Despite the wide variety of methods that have been used to define 'soluble' aerosol iron, our global-scale compilation reveals a remarkably consistent trend in the fractional solubility of aerosol iron as a function of total aerosol iron loading, with the great bulk of the data defining an hyperbolic trend. The hyperbolic trends that we observe for both global- and regional-scale data are adequately described by a simple two-component mixing model, whereby the fractional solubility of iron in the bulk aerosol reflects the conservative mixing of 'lithogenic' mineral dust (high FeT and low %FeS) and non-lithogenic 'combustion' aerosols (low FeT and high %FeS). An increasing body of empirical and model-based evidence points to anthropogenic fuel combustion as the major source of these non-lithogenic 'combustion' aerosols, implying that human emissions are a major determinant of the fractional solubility of iron in marine aerosols. The robust global-scale relationship between %FeS and FeT provides a simple heuristic method for estimating aerosol iron solubility at the regional to global scale.
Iron in the Sargasso Sea (Bermuda Atlantic Time-series Study region) during summer : eolian imprint, spatiotemporal variability, and ecological implications

(American Geophysical Union, 2005-10-13) Sedwick, Peter N. ; Church, Thomas M. ; Bowie, Andrew R. ; Marsay, Christopher M. ; Ussher, Simon J. ; Achilles, K. M. ; Lethaby, Paul ; Johnson, Rodney J. ; Sarin, M. M. ; McGillicuddy, Dennis J.

We report iron measurements for water column and aerosol samples collected in the Sargasso Sea during July-August 2003 (summer 2003) and April-May 2004 (spring 2004). Our data reveal a large seasonal change in the dissolved iron (dFe) concentration of surface waters in the Bermuda Atlantic Time-series Study region, from ∼1–2 nM in summer 2003, when aerosol iron concentrations were high (mean 10 nmol m−3), to ∼0.1–0.2 nM in spring 2004, when aerosol iron concentrations were low (mean 0.64 nmol m−3). During summer 2003, we observed an increase of ∼0.6 nM in surface water dFe concentrations over 13 days, presumably due to eolian iron input; an estimate of total iron deposition over this same period suggests an effective solubility of 3–30% for aerosol iron. Our summer 2003 water column profiles show potentially growth-limiting dFe concentrations (0.02–0.19 nM) coinciding with a deep chlorophyll maximum at 100–150 m depth, where phytoplankton biomass is typically dominated by Prochlorococcus during late summer.
Controls on dissolved cobalt in surface waters of the Sargasso Sea : comparisons with iron and aluminum

(American Geophysical Union, 2012-05-19) Shelley, Rachel U. ; Sedwick, Peter N. ; Bibby, Thomas S. ; Cabedo-Sanz, P. ; Church, Thomas M. ; Johnson, Rodney J. ; Macey, A. I. ; Marsay, Christopher M. ; Sholkovitz, Edward R. ; Ussher, Simon J. ; Worsfold, Paul J. ; Lohan, Maeve C.

Dissolved cobalt (dCo), iron (dFe) and aluminum (dAl) were determined in water column samples along a meridional transect (~31°N to 24°N) south of Bermuda in June 2008. A general north-to-south increase in surface concentrations of dFe (0.3–1.6 nM) and dAl (14–42 nM) was observed, suggesting that aerosol deposition is a significant source of dFe and dAl, whereas no clear trend was observed for near-surface dCo concentrations. Shipboard aerosol samples indicate fractional solubility values of 8–100% for aerosol Co, which are significantly higher than corresponding estimates of the solubility of aerosol Fe (0.44–45%). Hydrographic observations and analysis of time series rain samples from Bermuda indicate that wet deposition accounts for most (>80%) of the total aeolian flux of Co, and hence a significant proportion of the atmospheric input of dCo to our study region. Our aerosol data imply that the atmospheric input of dCo to the Sargasso Sea is modest, although this flux may be more significant in late summer. The water column dCo profiles reveal a vertical distribution that predominantly reflects ‘nutrient-type’ behavior, versus scavenged-type behavior for dAl, and a hybrid of nutrient- and scavenged-type behavior for dFe. Mesoscale eddies also appear to impact on the vertical distribution of dCo. The effects of biological removal of dCo from the upper water column were apparent as pronounced sub-surface minima (21 ± 4 pM dCo), coincident with maxima in Prochlorococcus abundance. These observations imply that Prochlorococcus plays a major role in removing dCo from the euphotic zone, and that the availability of dCo may regulate Prochlorococcus growth in the Sargasso Sea.
Dissolved iron transport pathways in the Ross Sea : influence of tides and horizontal resolution in a regional ocean model

( 2016-10) Mack, Stefanie L. ; Dinniman, Michael S. ; McGillicuddy, Dennis J. ; Sedwick, Peter N. ; Klinck, John M.

Phytoplankton production in the Ross Sea is regulated by the availability of dissolved iron (dFe), a limiting micro-nutrient, whose sources include Circumpolar Deep Water, sea ice melt, glacial melt, and benthic sources (sediment efflux and remineralization). We employ a passive tracer dye to model the benthic dFe sources and track pathways from deep areas of the continental shelf to the surface mixed layer in simulations with and without tidal forcing, and at 5 and 1.5km horizontal resolution. This, combined with dyes for each of the other dFe sources, provides an estimate of total dFe supply to surface waters. We find that tidal forcing increases the amount of benthic dye that covers the banks on the continental shelf. Calculations of mixed layer depth to define the surface ocean give similar average values over the shelf, but spatial patterns differ between simulations, particularly along the ice shelf front. Benthic dFe supply in simulations shows an increase with tidal forcing and a decrease with higher resolution. The changes in benthic dFe supply control the difference in total supply between simulations. Overall, the total dFe supply from simulations varies from 5.60 to 7.95 μmol m-2 yr-1, with benthic supply comprising 32-50%, comparing well with recent data and model synthesis. We suggest that including tides and using high horizontal resolution is important, especially when considering spatial variability of iron supply on the Ross Sea shelf.
The GEOTRACES Intermediate Data Product 2014

(Elsevier, 2015-04-16) Mawji, Edward ; Schlitzer, Reiner ; Dodas, Elena Masferrer ; Abadie, Cyril ; Abouchami, Wafa ; Anderson, Robert F. ; Baars, Oliver ; Bakker, Karel ; Baskaran, Mark ; Bates, Nicholas R. ; Bluhm, Katrin ; Bowie, Andrew R. ; Bown, Johann ; Boye, Marie ; Marie, Edward A. ; Branellec, Pierre ; Bruland, Kenneth W. ; Brzezinski, Mark A. ; Bucciarelli, Eva ; Buesseler, Ken O. ; Butler, Edward ; Cai, Pinghe ; Cardinal, Damien ; Casciotti, Karen L. ; Chaves, Joaquin E. ; Cheng, Hai ; Chever, Fanny ; Church, Thomas M. ; Colman, Albert S. ; Conway, Tim M. ; Croot, Peter L. ; Cutter, Gregory A. ; Baar, Hein J. W. de ; de Souza, Gregory F. ; Dehairs, Frank ; Deng, Feifei ; Dieu, Huong Thi ; Dulaquais, Gabriel ; Echegoyen-Sanz, Yolanda ; Edwards, R. Lawrence ; Fahrbach, Eberhard ; Fitzsimmons, Jessica N. ; Fleisher, Martin Q. ; Frank, Martin ; Friedrich, Jana ; Fripiat, Francois ; Galer, Stephen J. G. ; Gamo, Toshitaka ; Garcia Solsona, Ester ; Gerringa, Loes J. A. ; Godoy, Jose Marcus ; Gonzalez, Santiago ; Grossteffan, Emilie ; Hatta, Mariko ; Hayes, Christopher T. ; Heller, Maija Iris ; Henderson, Gideon M. ; Huang, Kuo-Fang ; Jeandel, Catherine ; Jenkins, William J. ; John, Seth G. ; Kenna, Timothy C. ; Klunder, Maarten ; Kretschmer, Sven ; Kumamoto, Yuichiro ; Laan, Patrick ; Labatut, Marie ; Lacan, Francois ; Lam, Phoebe J. ; Lannuzel, Delphine ; le Moigne, Frederique ; Lechtenfeld, Oliver J. ; Lohan, Maeve C. ; Lu, Yanbin ; Masqué, Pere ; McClain, Charles R. ; Measures, Christopher I. ; Middag, Rob ; Moffett, James W. ; Navidad, Alicia ; Nishioka, Jun ; Noble, Abigail E. ; Obata, Hajime ; Ohnemus, Daniel C. ; Owens, Stephanie A. ; Planchon, Frederic ; Pradoux, Catherine ; Puigcorbe, Viena ; Quay, Paul D. ; Radic, Amandine ; Rehkamper, Mark ; Remenyi, Tomas A. ; Rijkenberg, Micha J. A. ; Rintoul, Stephen R. ; Robinson, Laura F. ; Roeske, Tobias ; Rosenberg, Mark ; Rutgers van der Loeff, Michiel M. ; Ryabenko, Evgenia ; Saito, Mak A. ; Roshan, Saeed ; Salt, Lesley ; Sarthou, Geraldine ; Schauer, Ursula ; Scott, Peter M. ; Sedwick, Peter N. ; Sha, Lijuan ; Shiller, Alan M. ; Sigman, Daniel M. ; Smethie, William M. ; Smith, Geoffrey J. ; Sohrin, Yoshiki ; Speich, Sabrina ; Stichel, Torben ; Stutsman, Johnny ; Swift, James H. ; Tagliabue, Alessandro ; Thomas, Alexander L. ; Tsunogai, Urumu ; Twining, Benjamin S. ; van Aken, Hendrik M. ; van Heuven, Steven ; van Ooijen, Jan ; van Weerlee, Evaline ; Venchiarutti, Celia ; Voelker, Antje H. L. ; Wake, Bronwyn ; Warner, Mark J. ; Woodward, E. Malcolm S. ; Wu, Jingfeng ; Wyatt, Neil ; Yoshikawa, Hisayuki ; Zheng, Xin-Yuan ; Xue, Zichen ; Zieringer, Moritz ; Zimmer, Louise A.

The GEOTRACES Intermediate Data Product 2014 (IDP2014) is the first publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2013. It consists of two parts: (1) a compilation of digital data for more than 200 trace elements and isotopes (TEIs) as well as classical hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing a strongly inter-linked on-line atlas including more than 300 section plots and 90 animated 3D scenes. The IDP2014 covers the Atlantic, Arctic, and Indian oceans, exhibiting highest data density in the Atlantic. The TEI data in the IDP2014 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at cross-over stations. The digital data are provided in several formats, including ASCII spreadsheet, Excel spreadsheet, netCDF, and Ocean Data View collection. In addition to the actual data values the IDP2014 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering. Metadata about data originators, analytical methods and original publications related to the data are linked to the data in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2014 data providing section plots and a new kind of animated 3D scenes. The basin-wide 3D scenes allow for viewing of data from many cruises at the same time, thereby providing quick overviews of large-scale tracer distributions. In addition, the 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of observed tracer plumes, as well as for making inferences about controlling processes.
Iron supply and demand in an Antarctic shelf ecosystem

(John Wiley & Sons, 2015-10-08) McGillicuddy, Dennis J. ; Sedwick, Peter N. ; Dinniman, M. S. ; Arrigo, Kevin R. ; Bibby, Thomas S. ; Greenan, Blair J. W. ; Hofmann, Eileen E. ; Klinck, John M. ; Smith, Walker O. ; Mack, Stefanie L. ; Marsay, Christopher M. ; Sohst, Bettina M. ; van Dijken, Gert L.

The Ross Sea sustains a rich ecosystem and is the most productive sector of the Southern Ocean. Most of this production occurs within a polynya during the November–February period, when the availability of dissolved iron (dFe) is thought to exert the major control on phytoplankton growth. Here we combine new data on the distribution of dFe, high-resolution model simulations of ice melt and regional circulation, and satellite-based estimates of primary production to quantify iron supply and demand over the Ross Sea continental shelf. Our analysis suggests that the largest sources of dFe to the euphotic zone are wintertime mixing and melting sea ice, with a lesser input from intrusions of Circumpolar Deep Water and a small amount from melting glacial ice. Together these sources are in approximate balance with the annual biological dFe demand inferred from satellite-based productivity algorithms, although both the supply and demand estimates have large uncertainties.
Assessing phytoplankton nutritional status and potential impact of wet deposition in seasonally oligotrophic waters of the Mid‐Atlantic Bight

(John Wiley & Sons, 2018-04-06) Sedwick, Peter N. ; Bernhardt, Peter W. ; Mulholland, Margaret R. ; Najjar, Raymond G. ; Blumen, L. M. ; Sohst, Bettina M. ; Sookhdeo, C. ; Widner, Brittany

To assess phytoplankton nutritional status in seasonally oligotrophic waters of the southern Mid‐Atlantic Bight, and the potential for rain to stimulate primary production in this region during summer, shipboard bioassay experiments were performed using natural seawater and phytoplankton collected north and south of the Gulf Stream. Bioassay treatments comprised iron, nitrate, iron + nitrate, iron + nitrate + phosphate, and rainwater. Phytoplankton growth was inferred from changes in chlorophyll a, inorganic nitrogen, and carbon‐13 uptake, relative to unamended control treatments. Results indicated the greatest growth stimulation by iron + nitrate + phosphate, intermediate growth stimulation by rainwater, modest growth stimulation by nitrate and iron + nitrate, and no growth stimulation by iron. Based on these data and analysis of seawater and atmospheric samples, nitrogen was the proximate limiting nutrient, with a secondary limitation imposed by phosphorus. Our results imply that summer rain events increase new production in these waters by contributing nitrogen and phosphorus, with the availability of the latter setting the upper limit on rain‐stimulated new production.

Sedwick Peter N.

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