気候変動における海の役割(The role of the ocean in climate change)

2024-02-29 デラウェア大学 (UD)

＜関連情報＞

• https://www.udel.edu/udaily/2024/february/climate-change-indian-ocean-marine-heatwaves-mid-south-atlantic-bight-warming/
• https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL105363
• https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL106011

海洋熱波がアメリカ東海岸の大気-海洋CO2フラックスに与える影響 Impact of Marine Heatwaves on Air-Sea CO2 Flux Along the US East Coast

Kelsea Edwing, Zelun Wu, Wenfang Lu, Xinyu Li, Wei-Jun Cai, Xiao-Hai Yan
Geophysical Research Letters  ppublished: 02 January 2024
DOI:https://doi.org/10.1029/2023GL105363

Abstract

Marine heatwaves (MHWs) are extremely warm ocean temperature events that significantly affect marine environments, but their effects on the coastal carbonate system are still uncertain. In this study, we systematically quantify MHWs’ impacts on air-sea carbon dioxide (CO₂) flux anomalies (FCO₂′) in the Mid-Atlantic Bight (MAB) and South Atlantic Bight (SAB) from 1992 to 2020. During the longest MHW in both regions, oceanic CO₂ uptake capabilities substantially decreased, primarily due to significant increases in the seawater partial pressure of CO₂ (pCO_2sea). For all cases, MHWs played a more significant role in driving pCO_2sea changes in the MAB than the SAB, where non-thermal drivers dominated pCO_2sea variability. In the MAB, weakened wind speeds related to wintertime atmospheric perturbations increase ocean temperatures and pCO_2sea, further reducing CO₂ uptake during winter MHWs. This work is the first to connect extreme temperatures to coastal air-sea CO₂ fluxes. The reduction in CO₂ absorption noted during MHWs in this study has important implications for coastal regions to act as continued sinks for excess CO₂ emissions in the atmosphere.

Key Points

• Marine heatwaves (MHWs) primarily generated positive sea surface pCO₂ (pCO_2sea) anomalies in the Mid-Atlantic Bight (MAB) and South Atlantic Bight (SAB) but had a larger impact on air-sea CO₂ flux anomalies in the MAB
• Reduced wind speeds amplified MHW contributions during CO₂ sink months and counteracted them during CO₂ source months
• In the MAB, wintertime atmospheric perturbations related to zonal shifts in the jet stream produce slower wind speeds which aid in generating air-sea heat flux type MHW events that ultimately reduce oceanic CO₂ uptake

Plain Language Summary

The transfer of carbon dioxide (CO₂) between the atmosphere and ocean is sensitive to sea surface temperature (SST) changes because warmer SSTs increase the sea surface partial pressure of CO₂ and reduce the ocean’s ability to absorb CO₂ from the atmosphere. It is, therefore, conceivable that marine heatwaves (MHWs), which are extremely warm ocean temperature events, could modify how carbon moves between the ocean and the atmosphere. This study provides the first attempt to evaluate the impacts of MHWs on the air-sea CO₂ flux (FCO₂) anomalies along the US East Coast, encompassing the Mid-Atlantic Bight (MAB) and South Atlantic Bight (SAB) during 1992–2020. Both regions experienced reduced CO₂ absorption in response to the longest MHWs in each region. These extreme temperatures had a larger impact on CO₂ absorption in the MAB compared to the SAB, where non-temperature factors were more influential. The coastal ocean plays an important role in helping to mitigate human-induced climate change by absorbing excess CO₂ from the atmosphere. As such, the demonstrated reduced absorption of the ocean associated with MHWs in this study, which might also apply to other coastal locations, has vital implications for the efficiency of the ocean in offsetting global warming impacts.

熱帯南西インド洋における最近20年間の急激な海面上昇 Rapid Sea Level Rise in the Tropical Southwest Indian Ocean in the Recent Two Decades

Lei Huang, Wei Zhuang, Wenfang Lu, Yang Zhang, Deanna Edwing, Xiao-Hai Yan

First published: 27 December 2023　 

https://doi.org/10.1029/2023GL106011