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Abstract Glacierized coastal catchments of the Gulf of Alaska (GoA) are undergoing rapid hydrologic fluctuations in response to climate change. These catchments deliver dissolved and suspended inorganic and organic matter to nearshore marine environments, however, these glacierized coastal catchments are relatively understudied and little is known about total solute and particulate fluxes to the ocean. We present hydrologic, physical, and geochemical data collected during April–October 2019–2021 from 10 streams along gradients of glacial fed to non‐glacial (i.e., precipitation) fed, in one Southcentral and one Southeast Alaska region. Hydrologic data reveal that glaciers drive the seasonal runoff patterns. The ẟ18O signature and specific conductance show distinctive seasonal variations in stream water sources between the study regions apparently due to the large amounts of rain in Southeast Alaska. Total dissolved solids concentrations and yields were elevated in the Southcentral region, due to lithologic influence on dissolved loads, however, the hydroclimate is the primary driver of the timing of dissolved and suspended yields. We show the yields of dissolved organic carbon is higher and that the δ13CPOCis enriched in the Southeast streams illustrating contrasts in organic carbon export across the GoA. Finally, we illustrate how future yields of solutes and sediments to the GoA may change as watersheds evolve from glacial influenced to precipitation dominated. This integrated analysis provides insights into how watershed characteristics beyond glacier coverage control properties of freshwater inputs to the GoA and the importance of expanding study regions to multiple hydroclimate regimes.
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The Role of Glacier Erosion in Riverine Particulate Organic Carbon Export
Abstract Biospheric particulate organic carbon (POCbio) burial and rock petrogenic particulate organic carbon (POCpetro) oxidation are opposing long‐term controls on the global carbon cycle, sequestering and releasing carbon, respectively. Here, we examine how watershed glacierization impacts the POC source by assessing the concentration and isotopic composition (δ13C and Δ14C) of POC exported from four watersheds with 0%–49% glacier coverage across a melt season in Southeast Alaska. We used two mixing models (age‐weight percent and dual carbon isotope) to calculate concentrations of POCbioand POCpetrowithin the bulk POC pool. The fraction POCpetrocontribution was highest in the heavily glacierized watershed (age‐weight percent: 0.39 ± 0.05; dual isotope: 0.42 (0.37–0.47)), demonstrating a glacial source of POCpetroto fjords. POCpetrowas mobilized via glacier melt and subglacial flow, while POCbiowas largely flushed from the non‐glacierized landscape by rain. Flow normalized POCbioconcentrations exceeded POCpetroconcentrations for all streams, but surprisingly were highest in the heavily glacierized watershed (mean: 0.70 mgL−1; range 0.16–1.41 mgL−1), suggesting that glacier rivers can contribute substantial POCbioto coastal waters. Further, the most heavily glacierized watershed had the highest sediment concentration (207 mgL−1; 7–708 mgL−1), and thus may facilitate long‐term POCbioprotection via sediment burial in glacier‐dominated fjords. Our results suggest that continuing glacial retreat will decrease POC concentrations and increase POCbio:POCpetroexported from currently glacierized watersheds. Glacier retreat may thus decrease carbon storage in marine sediments and provide a positive feedback mechanism to climate change that is sensitive to future changes in POCpetrooxidation.
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- Award ID(s):
- 1757348
- PAR ID:
- 10476286
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Global Biogeochemical Cycles
- Volume:
- 37
- Issue:
- 11
- ISSN:
- 0886-6236
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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