Whitmore
Laura M.
Whitmore
Laura M.
No Thumbnail Available
Search Results
Now showing
1 - 4 of 4
-
ArticleStrong margin influence on the Arctic Ocean Barium Cycle revealed by pan‐Arctic synthesis(American Geophysical Union, 2022-03-22) Whitmore, Laura M. ; Shiller, Alan M. ; Horner, Tristan J. ; Xiang, Yang ; Auro, Maureen E. ; Bauch, Dorothea ; Dehairs, Frank ; Lam, Phoebe J. ; Li, Jingxuan ; Maldonado, Maria T. ; Mears, Chantal ; Newton, Robert ; Pasqualini, Angelica ; Planquette, Helene ; Rember, Robert ; Thomas, HelmuthEarly studies revealed relationships between barium (Ba), particulate organic carbon and silicate, suggesting applications for Ba as a paleoproductivity tracer and as a tracer of modern ocean circulation. But, what controls the distribution of barium (Ba) in the oceans? Here, we investigated the Arctic Ocean Ba cycle through a one-of-a-kind data set containing dissolved (dBa), particulate (pBa), and stable isotope Ba ratio (δ138Ba) data from four Arctic GEOTRACES expeditions conducted in 2015. We hypothesized that margins would be a substantial source of Ba to the Arctic Ocean water column. The dBa, pBa, and δ138Ba distributions all suggest significant modification of inflowing Pacific seawater over the shelves, and the dBa mass balance implies that ∼50% of the dBa inventory (upper 500 m of the Arctic water column) was supplied by nonconservative inputs. Calculated areal dBa fluxes are up to 10 μmol m−2 day−1 on the margin, which is comparable to fluxes described in other regions. Applying this approach to dBa data from the 1994 Arctic Ocean Survey yields similar results. The Canadian Arctic Archipelago did not appear to have a similar margin source; rather, the dBa distribution in this section is consistent with mixing of Arctic Ocean-derived waters and Baffin Bay-derived waters. Although we lack enough information to identify the specifics of the shelf sediment Ba source, we suspect that a sedimentary remineralization and terrigenous sources (e.g., submarine groundwater discharge or fluvial particles) are contributors.
-
ArticleThe transpolar drift as a source of riverine and shelf-derived trace elements to the central Arctic Ocean(American Geophysical Union, 2020-04-08) Charette, Matthew A. ; Kipp, Lauren ; Jensen, Laramie T. ; Dabrowski, Jessica S. ; Whitmore, Laura M. ; Fitzsimmons, Jessica N. ; Williford, Tatiana ; Ulfsbo, Adam ; Jones, Elizabeth M. ; Bundy, Randelle M. ; Vivancos, Sebastian M. ; Pahnke, Katharina ; John, Seth G. ; Xiang, Yang ; Hatta, Mariko ; Petrova, Mariia V. ; Heimbürger, Lars-Eric ; Bauch, Dorothea ; Newton, Robert ; Pasqualini, Angelica ; Agather, Alison ; Amon, Rainer M. W. ; Anderson, Robert F. ; Andersson, Per S. ; Benner, Ronald ; Bowman, Katlin ; Edwards, R. Lawrence ; Gdaniec, Sandra ; Gerringa, Loes J. A. ; González, Aridane G. ; Granskog, Mats A. ; Haley, Brian ; Hammerschmidt, Chad R. ; Hansell, Dennis A. ; Henderson, Paul B. ; Kadko, David C. ; Kaiser, Karl ; Laan, Patrick ; Lam, Phoebe J. ; Lamborg, Carl H. ; Levier, Martin ; Li, Xianglei ; Margolin, Andrew R. ; Measures, Christopher I. ; Middag, Rob ; Millero, Frank J. ; Moore, Willard S. ; Paffrath, Ronja ; Planquette, Helene ; Rabe, Benjamin ; Reader, Heather ; Rember, Robert ; Rijkenberg, Micha J. A. ; Roy-Barman, Matthieu ; van der Loeff, Michiel Rutgers ; Saito, Mak A. ; Schauer, Ursula ; Schlosser, Peter ; Sherrell, Robert M. ; Shiller, Alan M. ; Slagter, Hans ; Sonke, Jeroen E. ; Stedmon, Colin ; Woosley, Ryan J. ; Valk, Ole ; van Ooijen, Jan ; Zhang, RuifengA major surface circulation feature of the Arctic Ocean is the Transpolar Drift (TPD), a current that transports river‐influenced shelf water from the Laptev and East Siberian Seas toward the center of the basin and Fram Strait. In 2015, the international GEOTRACES program included a high‐resolution pan‐Arctic survey of carbon, nutrients, and a suite of trace elements and isotopes (TEIs). The cruises bisected the TPD at two locations in the central basin, which were defined by maxima in meteoric water and dissolved organic carbon concentrations that spanned 600 km horizontally and ~25–50 m vertically. Dissolved TEIs such as Fe, Co, Ni, Cu, Hg, Nd, and Th, which are generally particle‐reactive but can be complexed by organic matter, were observed at concentrations much higher than expected for the open ocean setting. Other trace element concentrations such as Al, V, Ga, and Pb were lower than expected due to scavenging over the productive East Siberian and Laptev shelf seas. Using a combination of radionuclide tracers and ice drift modeling, the transport rate for the core of the TPD was estimated at 0.9 ± 0.4 Sv (106 m3 s−1). This rate was used to derive the mass flux for TEIs that were enriched in the TPD, revealing the importance of lateral transport in supplying materials beneath the ice to the central Arctic Ocean and potentially to the North Atlantic Ocean via Fram Strait. Continued intensification of the Arctic hydrologic cycle and permafrost degradation will likely lead to an increase in the flux of TEIs into the Arctic Ocean.
-
ArticleBarium in seawater: dissolved distribution, relationship to silicon, and barite saturation state determined using machine learning(Copernicus Publications, 2023-09-13) Mete, Oyku Z. ; Subhas, Adam V. ; Kim, Heather H. ; Dunlea, Ann G. ; Whitmore, Laura M. ; Shiller, Alan M. ; Gilbert, Melissa ; Leavitt, William D. ; Horner, Tristan J.Barium is widely used as a proxy for dissolved silicon and particulate organic carbon fluxes in seawater. However, these proxy applications are limited by insufficient knowledge of the dissolved distribution of Ba ([Ba]). For example, there is significant spatial variability in the barium–silicon relationship, and ocean chemistry may influence sedimentary Ba preservation. To help address these issues, we developed 4095 models for predicting [Ba] using Gaussian process regression machine learning. These models were trained to predict [Ba] from standard oceanographic observations using GEOTRACES data from the Arctic, Atlantic, Pacific, and Southern oceans. Trained models were then validated by comparing predictions against withheld [Ba] data from the Indian Ocean. We find that a model trained using depth, temperature, and salinity, as well as dissolved dioxygen, phosphate, nitrate, and silicate, can accurately predict [Ba] in the Indian Ocean with a mean absolute percentage deviation of 6.0 %. We use this model to simulate [Ba] on a global basis using these same seven predictors in the World Ocean Atlas. The resulting [Ba] distribution constrains the Ba budget of the ocean to 122(±7) × 1012 mol and reveals oceanographically consistent variability in the barium–silicon relationship. We then calculate the saturation state of seawater with respect to barite. This calculation reveals systematic spatial and vertical variations in marine barite saturation and shows that the ocean below 1000 m is at equilibrium with respect to barite. We describe a number of possible applications for our model outputs, ranging from use in mechanistic biogeochemical models to paleoproxy calibration. Our approach demonstrates the utility of machine learning in accurately simulating the distributions of tracers in the sea and provides a framework that could be extended to other trace elements. Our model, the data used in training and validation, and global outputs are available in Horner and Mete (2023, https://doi.org/10.26008/1912/bco-dmo.885506.2).
-
ArticleRadium isotopes as tracers of shelf-basin exchange processes in the eastern Arctic Ocean(American Geophysical Union, 2023-12-27) Kipp, Lauren ; Charette, Matthew A. ; Robbins, Alyssa ; Pnyushkov, Andrey ; Polyakov, Igor V. ; Whitmore, Laura M.Radium isotopes, which are sourced from sediments, are useful tools for studying potential climate-driven changes in the transfer of shelf-derived elements to the open Arctic Ocean. Here we present observations of radium-228 and radium-226 from the Siberian Arctic, focusing on the shelf-basin boundary north of the Laptev and East Siberian Seas. Water isotopes and nutrients are used to deconvolve the contributions from different water masses in the study region, and modeled currents and water parcel back-trajectories provide insights on water pathways and residence times. High radium levels and fractions of meteoric water, along with modeled water parcel back-trajectories, indicate that shelf- and river-influenced water left the East Siberian Shelf around 170°E in 2021; this is likely where the Transpolar Drift was entering the central Arctic. A transect extending from the East Siberian Slope into the basin is used to estimate a radium-228 flux of 2.67 × 107 atoms m−2 d−1 (possible range of 1.23 × 107–1.04 × 108 atoms m−2 d−1) from slope sediments, which is comparable to slope fluxes in other regions of the world. A box model is used to determine that the flux of radium-228 from the Laptev and East Siberian Shelves is 9.03 × 107 atoms m−2 d−1 (possible range of 3.87 × 107–1.56 × 108 atoms m−2 d−1), similar to previously estimated fluxes from the Chukchi Shelf. These three shelves contribute a disproportionately high amount of radium to the Arctic, highlighting their importance in regulating the chemistry of Arctic surface waters.