Simulated Impact of Glacial Runoff on CO₂ Uptake in the Gulf of Alaska

Abstract

The Gulf of Alaska (GOA) receives substantial summer freshwater runoff from glacial meltwater. The alkalinity of this runoff is highly dependent on the glacial source and can modify the coastal carbon cycle. We use a regional ocean biogeochemical model to simulate CO2 uptake in the GOA under different alkalinity‐loading scenarios. The GOA is identified as a current net sink of carbon, though low‐alkalinity tidewater glacial runoff suppresses summer coastal carbon uptake. Our model shows that increasing the alkalinity generates an increase in annual CO2 uptake of 1.9–2.7 TgC/yr. This transition is comparable to a projected change in glacial runoff composition (i.e., from tidewater to land‐terminating) due to continued climate warming. Our results demonstrate an important local carbon‐climate feedback that can significantly increase coastal carbon uptake via enhanced air‐sea exchange, with potential implications to the coastal ecosystems in glaciated areas around the world.

A regional hindcast model simulating ecosystem dynamics, inorganic carbon chemistry and ocean acidification in the Gulf of Alaska

“…As this region continuous to rapidly deglaciate (Arendt et al, 2002;Larsen et al, 2007;O'Neel et al, 2005), not only the amount of freshwater discharge will increase (Beamer et al, 2017), but most of the glaciers surrounding the GOA will recede away 15 from the ocean and into higher elevations (Huss and Hock, 2015), resulting in a change of the biogeochemical composition of freshwater. This and previous studies have shown that freshwater discharge is the largest driver of the nearshore inorganic carbon dynamics in summer and fall, and is known to exacerbate the effects of ocean acidification Siedlecki et al, 2017;Pilcher et al, 2018). Understanding the composition of freshwater sources is, therefore, particularly important for the study of long-term trends of ocean acidification in the GOA-LME.…”

“…The only other regional biogeochemical model with an oceanic carbon cycle Pilcher et al, 2018) Our simulation results give new and important insights for months of the year that lack in situ inorganic carbon observations. For example, the majority of the near-bottom water along the Seward Line is seasonally under-saturated with regard to aragonite between June and January.…”

“…In our model, the aragonite saturation horizon is shallower throughout the year, thereby causing aragonite undersaturation across wider areas on the shelf. A thorough model inter-comparison study would need to be done to understand how the new features of our model set-up have affected and potentially improved the modeling results overSiedlecki et al (2017) andPilcher et al (2018).…”

Influence of Glacial Meltwater on Summer Biogeochemical Cycles in Scoresby Sund, East Greenland

“…With respect to TA, the source of meltwater is particularly important. Runoff from land-terminating glaciers carries higher TA concentrations due to stronger interaction with the bedrock than the meltwater from marine-terminating glaciers (Anderson et al, 2000;Brown, 2002;Reisdorph and Mathis, 2014;Pilcher et al, 2018). Because our TA freshwater endmember concentration was almost five times those obtained by Rysgaard et al (2012) and Meire et al (2015) in Godthåbsfjord, we suspect that the contribution of meltwater from land-terminating glaciers in Scoresby Sund is higher than in Godthåbsfjord.…”

A regional hindcast model simulating ecosystem dynamics, inorganic carbon chemistry, and ocean acidification in the Gulf of Alaska

“…The currency of biomass and productivity in the model is nitrogen. Organic nitrogen is converted into organic carbon following the Redfield ratio of 106 : 16 (Redfield et al, 1963). DIC and TA are state variables and dictate the inorganic carbon system.…”