Abstract
Manifestations of climate change in the Arctic are numerous and include hydrological cycle intensification and permafrost thaw, both expected as a result of atmospheric and surface warming. Across the terrestrial Arctic dissolved organic carbon (DOC) entrained in arctic rivers may be providing a carbon subsidy to coastal food webs. Yet, data from field sampling is too often of limited duration to confidently ascertain impacts of climate change on freshwater and DOC flows to coastal waters. This study applies numerical modeling to investigate trends in freshwater and DOC exports from land to Elson Lagoon in Northwest Alaska over the period 1981–2020. While the modeling approach has limitations, the results point to significant increases in freshwater and DOC exports to the lagoon over the past four decades. The model simulation reveals significant increases in surface, subsurface (suprapermafrost), and total freshwater exports. Significant increases are also noted in surface and subsurface DOC production and export, influenced by warming soils and associated active-layer thickening. The largest changes in subsurface components are noted in September, which has experienced a ∼50% increase in DOC export emanating from suprapermafrost flow. Direct coastal suprapermafrost freshwater and DOC exports in late summer more than doubled between the first and last five years of the simulation period, with a large anomaly in September 2019 representing a more than fourfold increase over September direct coastal export during the early 1980s. These trends highlight the need for dedicated measurement programs that will enable improved understanding of climate change impacts on coastal zone processes in this data sparse region of Northwest Alaska.
Highlights
Arctic amplification is one of many hallmarks of earth’s changing climate (Serreze et al 2009)
Water yield is a major control on dissolved organic carbon (DOC) loaded into arctic rivers (Raymond et al 2007, Holmes et al 2012), and while the bulk of riverine DOC export occurs during the freshet, suprapermafrost groundwater flow can supply substantial quantities of DOC
This study describes a decades long trend in freshwater and DOC export to Elson Lagoon, quantified by a model simulation, that supports the hypothesis of increasing fluxes, and adds to a growing body of evidence that hydrologic cycle intensification and permafrost thaw are impacting coastal ecosystems in northern Alaska
Summary
Arctic amplification is one of many hallmarks of earth’s changing climate (Serreze et al 2009). Field studies near Utqiagvik (formerly Barrow), AK are providing baseline estimates of freshwater and nutrient flows to adjacent coastal waters (Lougheed et al 2020) Such focused studies, while providing important data for understanding coastal zone structure and function and, in turn, its ecosystem services, are limited in their utility for assessing how terrestrial exports of freshwater and nutrients are changing under the influences related to climate warming. Coastal waters in northern Alaska receive freshwater from rivers rich in organic matter (McClelland et al 2014), with much of the influx occurring during the spring freshet that follows snowmelt This flux of water-borne nutrients including dissolved organic carbon (DOC) strongly influences coastal ocean food web dynamics (Dunton et al 2012, McMeans et al 2013, Connelly et al 2015). Water yield (runoff) is a major control on DOC loaded into arctic rivers (Raymond et al 2007, Holmes et al 2012), and while the bulk of riverine DOC export occurs during the freshet, suprapermafrost groundwater flow can supply substantial quantities of DOC
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