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1. Alaskan Glacial Dust Is an Important Iron Source to Surface Waters of the Gulf of Alaska

   https://doi.org/10.1029/2023GL106778  

   Crusius, John; Lao, Carsten_A; Holmes, Thomas_M; Murray, James_W (June 2024, Geophysical Research Letters)

   Abstract This work evaluates glacial dust as a source of sediment, and associated iron (Fe), to the Fe‐limited Gulf of Alaska (GoA). A reanalysis of GoA sediment data, using rare earth elements and thorium as provenance tracers, suggests a flux to the ocean surface of Copper River (AK) glacial dust, and associated Fe, that is comparable to the flux of dust from Asia, at least 1,000 km from the narrow mountain valley glacial dust source area. This work suggests dust from Asia may not be the largest source of Fe to the GoA. Dust models fail to accurately simulate this glacial dust transport because their coarse resolution underestimates wind speeds, and the dust flux. This work suggests that glacial dust fluxes may have been important in the geologic past (e.g., the last glacial maximum) from locations where there was more extensive coverage by glaciers than at present. 

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2. Toward Constraining Sources of Lithogenic Metals in the Northern Gulf of Mexico

   https://doi.org/10.1029/2022JC018523  

   Hayes, Christopher T.; Shiller, Alan M.; Milroy, Scott P. (April 2022, Journal of Geophysical Research: Oceans)

   Abstract North African dust is known to be deposited in the Gulf of Mexico, but its deposition rate and associated supply of lithogenic dissolved metals, such as the abiotic metal thorium or the micronutrient metal iron, have not been well‐quantified.²³²Th is an isotope with similar sources as iron and its input can be quantified using radiogenic²³⁰Th. By comparing dissolved²³²Th fluxes at three sites in the northern Gulf of Mexico with upwind sites in the North Atlantic, we place an upper bound on North African dust contributions to²³²Th and Fe in the Gulf of Mexico, which is about 30% of the total input. Precision on this bound is hindered by uncertainty in the relative rates of dust deposition in the North Atlantic and the northern Gulf of Mexico. Based on available radium data, shelf sources, including rivers, submarine groundwater discharge, and benthic sedimentary releases are likely as important if not more important than dust in the budget of lithogenic metals in the Gulf of Mexico. In other words, it is likely there is no one dominant source of Th and Fe in the Gulf of Mexico. Finally, our estimated Fe input in the northern Gulf of Mexico implies an Fe residence time of less than 6 months, similar to that in the North Atlantic despite significantly higher supply rates in the Gulf of Mexico. 

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3. Contribution of Fresh Submarine Groundwater Discharge to the Gulf of Alaska

   https://doi.org/10.1029/2023WR034912  

   Russo, A A; Boutt, D F; Munk, L A; Jenckes, J (July 2023, Water Resources Research)

   Abstract High latitude mountain environments are experiencing disproportionately adverse effects from climate change. The Gulf of Alaska (GoA) region is an embodiment of this change, particularly concerning a shifting hydrologic balance. Even so, the magnitude and contribution of fresh submarine groundwater discharge (fresh SGD) remains virtually unexplored within the region, though it has gained increasing attention globally due to its chemical significance and influence on coastal ecosystems. Here we provide the first regional estimates of fresh SGD to the GoA using two established water balance approaches. This is an effective way to distinguish the contribution of terrestrially derived fresh SGD, rather than the more commonly quantified total SGD which includes discharge that is driven by marine forces such as sea‐level oscillations and density gradients. We compare the approaches and assess their capabilities in computing the magnitude of fresh SGD over a large regional scale. Mean annual fresh SGD flux ranges between 26.5 and 86.8 km³ yr⁻¹to the GoA, equivalent to 3.5%–11.4% of the total freshwater discharge. Contributions are highest in the Southeastern panhandle and lowest in the Cook Inlet basin, with the highest area normalized contribution occurring in the Prince William Sound. Fresh SGD exhibits high spatial and temporal variability throughout the region. Although freshwater discharge to the GoA is investigated considerably, the importance of fresh SGD has, thus far, been overlooked. 

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4. Hydroclimate Drives Seasonal Riverine Export Across a Gradient of Glacierized High‐Latitude Coastal Catchments

   https://doi.org/10.1029/2022WR033305  

   Jenckes, J.; Munk, L. A.; Ibarra, D. E.; Boutt, D. F.; Fellman, J.; Hood, E. (April 2023, Water Resources Research)

   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 δ¹³C_POCis 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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5. Methods for Combining Ichthyoplankton Datasets for Predicting Annual Larval Fish Abundances in the Gulf of Alaska

   Block, L N; Hopcroft, R R; Rogers, L A (May 2024, NOAA Technical Memorandum)

   NOAA’s Alaska Fisheries Science Center’s (AFSC) Ecosystems and Fisheries-Oceanography Coordinated Investigations (EcoFOCI) program has collected spring ichthyoplankton abundance data in the Gulf of Alaska since 1981. Collections were made nearly annually until 2011 when sampling was reduced to only odd years. This dataset is used to better understand population recruitment of major fish species in the GOA and provides early warning of potential year-class strength to inform fisheries management. However, gaps in the time series during even years have made it more difficult to interpret the interannual variability of ichthyoplankton abundance in such a dynamic ecosystem. Recent collaboration with the Northern Gulf of Alaska Long Term Ecological Research (NGA LTER) program has allowed for additional spring sampling of ichthyoplankton in the GOA annually since 2018. Larval fish data collected by the NGA LTER were combined with EcoFOCI data and used to estimate abundance in years when EcoFOCI had no field presence in the GOA. Five taxa were determined to be suitable for this approach based on their percent occurrence in both surveys. A generalized additive model (GAM) was fit to ichthyoplankton data from 1981 to 2022 collected by both EcoFOCI and NGA LTER and used to predict larval abundances in 2018, 2020, and 2022. For each species, models with two different error distributions were compared and shown to produce similar predictions of larval abundance. This report provides a model framework for predicting interannual larval fish abundance while controlling for differences in sampling methodologies, timing, and location, and identifies a subset of taxa for which this framework is currently appropriate. As additional years of concurrent sampling are added in future, this approach has the potential to improve our understanding of interannual variation in ichthyoplankton dynamics and provide more comprehensive indicators for ecosystem-based fisheries management. 

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