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[ACG39-13] Impacts of Riverine Carbon and Nutrient Delivery on Arctic Ocean Acidification
Keywords:Ocean Acidification, Riverine Fluxes, Model Simulation, Arctic Ocean
Introduction
Rapid environmental changes are happening in the Arctic Ocean, such as extensive sea ice retreat, seawater warming, ocean acidification (OA). The effect of climate change on land also affects the Arctic Ocean by increasing riverine biogeochemical delivery (carbon and nutrient) via runoff increase, permafrost thaw, and tree-line advance[1]. Changes in riverine delivery of carbon and nutrient may affect the primary production, air-sea CO2 fluxes, and OA significantly. It was revealed that aragonite undersaturation (caused by OA) has been continued for more than one decade since 2006 in the surface waters of Arctic Ocean[2]. However, it is still unclear to what extent the delivery of riverine biogeochemical fluxes (R_BGC) has an impact on OA, as well on primary production and marine ecosystem in the Arctic Ocean.
Data & Method
By using a Pan-Arctic Sea Ice-Ocean Model (COCO) coupled to an Arctic and North Pacific Model for Lower-trophic Marine Ecosystem with Carbonate Chemistry (Arctic NEMURO-C), we conducted sensitivity experiments to understand the impact of riverine biogeochemical delivery on OA (including indexes of pH, aragonite saturation state: ΩAr) in several Arctic sub-regions for 1979-2018. Four experiments are composed of 1. Without R_BGC, 2. With only R_Carbon (Riverine TA and DIC fluxes), 3. With only R_Nut (Riverine Nitrate and Silicate fluxes), 4. With R_BGC. Monthly climatological riverine carbon and nutrient data were obtained from the Arctic Great Rivers Observatory (ArcticGRO). Monthly climatological freshwater fluxes known as R-ArcticNET were obtained from the Arctic Ocean Model Inter-comparison Project (AOMIP).
Results & Discussion
Compared with result in the case 1 (Without R_BGC case: only riverine freshwater fluxes were involved), it is found that R_BGC increases pH and ΩAr in waters shallower than ~100 m in almost the whole Arctic Ocean. In surface waters of the central Arctic (latitude > 83°N), mean positive anomalies for 1989-2018 in pH and ΩAr by R_BGC are ~0.01 and ~0.06, respectively, which is mostly due to delivery of R_Carbon in this region where the effect of R_Nut delivery is negligible.
Relatively large increases in pH and ΩAr by R_BGC are found in surface waters near the coastal regions, where large rivers enter into the Arctic Ocean, as well along the Lomonosov Ridge, which reflects the distribution pattern of transpolar drift that transports river waters further into the central Arctic. The largest positive anomalies of pH and ΩAr by R_BGC are found in the surface waters of Laptev Sea and Kara Sea where simulation with R_BGC causes a higher pH by ~0.1 and higher ΩAr by ~0.1. In these seas, delivery of R_Nut attributes up to ~20% of pH increment and ~10% of ΩAr increment, which is a consequence of enhanced primary productivity by the riverine nutrient supply.
References:
[1] Terhaar et al., (2019). Global Biogeochemical Cycles, 33, 1048–1070.
[2] Zhang, Y. et al., (2020). Geophysical Research Letters, 47, e60119.
Rapid environmental changes are happening in the Arctic Ocean, such as extensive sea ice retreat, seawater warming, ocean acidification (OA). The effect of climate change on land also affects the Arctic Ocean by increasing riverine biogeochemical delivery (carbon and nutrient) via runoff increase, permafrost thaw, and tree-line advance[1]. Changes in riverine delivery of carbon and nutrient may affect the primary production, air-sea CO2 fluxes, and OA significantly. It was revealed that aragonite undersaturation (caused by OA) has been continued for more than one decade since 2006 in the surface waters of Arctic Ocean[2]. However, it is still unclear to what extent the delivery of riverine biogeochemical fluxes (R_BGC) has an impact on OA, as well on primary production and marine ecosystem in the Arctic Ocean.
Data & Method
By using a Pan-Arctic Sea Ice-Ocean Model (COCO) coupled to an Arctic and North Pacific Model for Lower-trophic Marine Ecosystem with Carbonate Chemistry (Arctic NEMURO-C), we conducted sensitivity experiments to understand the impact of riverine biogeochemical delivery on OA (including indexes of pH, aragonite saturation state: ΩAr) in several Arctic sub-regions for 1979-2018. Four experiments are composed of 1. Without R_BGC, 2. With only R_Carbon (Riverine TA and DIC fluxes), 3. With only R_Nut (Riverine Nitrate and Silicate fluxes), 4. With R_BGC. Monthly climatological riverine carbon and nutrient data were obtained from the Arctic Great Rivers Observatory (ArcticGRO). Monthly climatological freshwater fluxes known as R-ArcticNET were obtained from the Arctic Ocean Model Inter-comparison Project (AOMIP).
Results & Discussion
Compared with result in the case 1 (Without R_BGC case: only riverine freshwater fluxes were involved), it is found that R_BGC increases pH and ΩAr in waters shallower than ~100 m in almost the whole Arctic Ocean. In surface waters of the central Arctic (latitude > 83°N), mean positive anomalies for 1989-2018 in pH and ΩAr by R_BGC are ~0.01 and ~0.06, respectively, which is mostly due to delivery of R_Carbon in this region where the effect of R_Nut delivery is negligible.
Relatively large increases in pH and ΩAr by R_BGC are found in surface waters near the coastal regions, where large rivers enter into the Arctic Ocean, as well along the Lomonosov Ridge, which reflects the distribution pattern of transpolar drift that transports river waters further into the central Arctic. The largest positive anomalies of pH and ΩAr by R_BGC are found in the surface waters of Laptev Sea and Kara Sea where simulation with R_BGC causes a higher pH by ~0.1 and higher ΩAr by ~0.1. In these seas, delivery of R_Nut attributes up to ~20% of pH increment and ~10% of ΩAr increment, which is a consequence of enhanced primary productivity by the riverine nutrient supply.
References:
[1] Terhaar et al., (2019). Global Biogeochemical Cycles, 33, 1048–1070.
[2] Zhang, Y. et al., (2020). Geophysical Research Letters, 47, e60119.