Tamborski Joseph

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  • Article
    Revisiting 228Th as a tool for determining sedimentation and mass accumulation rates
    (Elsevier, 2022-07-12) Tamborski, Joseph ; Cai, Pinghe ; Eagle, Meagan ; Henderson, Paul B. ; Charette, Matthew A.
    The use of 228Th has seen limited application for determining sedimentation and mass accumulation rates in coastal and marine environments. Recent analytical advances have enabled rapid, precise measurements of particle-bound 228Th using a radium delayed coincidence counting system (RaDeCC). Herein we review the 228Th cycle in the marine environment and revisit the historical use of 228Th as a tracer for determining sediment vertical accretion and mass accumulation rates in light of new measurement techniques. Case studies comparing accumulation rates from 228Th and 210Pb are presented for a micro-tidal salt marsh and a marginal sea environment. 228Th and 210Pb have been previously measured in mangrove, deltaic, continental shelf and ocean basin environments, and a literature synthesis reveals that 228Th (measured via alpha or gamma spectrometry) derived accumulation rates are generally equal to or greater than estimates derived from 210Pb, reflecting different integration periods. Use of 228Th is well-suited for shallow (<15 cm) cores over decadal timescales. Application is limited to relatively homogenous sediment profiles with minor variations in grain size and minimal bioturbation. When appropriate conditions are met, complimentary use of 228Th and 210Pb can demonstrate that the upper layers of a core are undisturbed and can improve spatial coverage in mapping accumulation rates due to the higher sample throughput for sediment 228Th.
  • Article
    Radium isotopes as submarine groundwater discharge (SGD) tracers: review and recommendations
    (Elsevier, 2021-05-14) Garcia-Orellana, Jordi ; Rodellas, Valenti ; Tamborski, Joseph ; Diego-Feliu, Marc ; van Beek, Pieter ; Weinstein, Yishai ; Charette, Matthew A. ; Alorda-Kleinglass, Aaron ; Michael, Holly A. ; Stieglitz, Thomas ; Scholten, Jan C.
    Submarine groundwater discharge (SGD) is now recognized as an important process of the hydrological cycle worldwide and plays a major role as a conveyor of dissolved compounds to the ocean. Naturally occurring radium isotopes (223Ra, 224Ra, 226Ra and 228Ra) are widely employed geochemical tracers in marine environments. Whilst Ra isotopes were initially predominantly applied to study open ocean processes and fluxes across the continental margins, their most common application in the marine environment has undoubtedly become the identification and quantification of SGD. This review focuses on the application of Ra isotopes as tracers of SGD and associated inputs of water and solutes to the coastal ocean. In addition, we review i) the processes controlling Ra enrichment and depletion in coastal groundwater and seawater; ii) the systematics applied to estimate SGD using Ra isotopes and iii) we summarize additional applications of Ra isotopes in groundwater and marine studies. We also provide some considerations that will help refine SGD estimates and identify the critical knowledge gaps and research needs related to the current use of Ra isotopes as SGD tracers.
  • Article
    Pore water exchange-driven inorganic carbon export from intertidal salt marshes
    (Association for the Sciences of Limnology and Oceanography, 2021-03-11) Tamborski, Joseph ; Eagle, Meagan ; Kurylyk, Barret L. ; Kroeger, Kevin D. ; Wang, Zhaoihui Aleck ; Henderson, Paul B. ; Charette, Matthew A.
    Respiration in intertidal salt marshes generates dissolved inorganic carbon (DIC) that is exported to the coastal ocean by tidal exchange with the marsh platform. Understanding the link between physical drivers of water exchange and chemical flux is a key to constraining coastal wetland contributions to regional carbon budgets. The spatial and temporal (seasonal, annual) variability of marsh pore water exchange and DIC export was assessed from a microtidal salt marsh (Sage Lot Pond, Massachusetts). Spatial variability was constrained from 224Ra : 228Th disequilibria across two hydrologic units within the marsh sediments. Disequilibrium between the more soluble 224Ra and its sediment-bound parent 228Th reveals significant pore water exchange in the upper 5 cm of the marsh surface (0–36 L m−2 d−1) that is most intense in low marsh elevation zones, driven by tidal overtopping. Surficial sediment DIC transport ranges from 0.0 to 0.7 g C m−2 d−1. The sub-surface sediment horizon intersected by mean low tide was disproportionately impacted by tidal pumping (20–80 L m−2 d−1) and supplied a seasonal DIC flux of 1.7–5.4 g C m−2 d−1. Export exceeded 10 g C m−2 d−1 for another marsh unit, demonstrating that fluxes can vary substantially across salt marshes under similar conditions within the same estuary. Seasonal and annual variability in marsh pore water exchange, constrained from tidal time-series of radium isotopes, was driven in part by variability in mean sea level. Rising sea levels will further inundate high marsh elevation zones, which may lead to greater DIC export.