New method estimates translatitudinal Atlantic freshwater transport

Researchers from the Institute of Atmospheric Physics, Chinese Academy of Sciences and Xiamen University have developed an indirect method to estimate Atlantic meridional freshwater transport (AMFT) at different latitudes. The study was published in Geophysical Research Letters.

The oceans, which contain 97% of Earth’s water, play an important role in the global water cycle. We exchange freshwater with the atmosphere, land, and cryosphere, and these exchanges are directly reflected in changes in ocean salinity.

As a result, changes in ocean salinity are often expressed as changes in ocean freshwater in theoretical studies. This approach provides a unified framework for estimating the Earth’s water cycle and understanding the dynamics of global water systems.

The redistribution of freshwater in the oceans, driven primarily by freshwater transport, is an important part of the Earth’s water cycle. The Atlantic Ocean, in particular, plays an important role. This is because changes in freshwater levels in the subpolar North Atlantic not only reflect regional freshwater exchange but can also affect global ocean circulation.

However, current observations of AMFT are limited to a few specific latitudes (between 26°N and approximately 55°N) due to the high costs associated with establishing observation arrays. This limited coverage significantly hinders our understanding of AMFT changes and the mechanisms behind them.

Researchers addressed the ocean’s freshwater budget by analyzing ocean freshwater content derived from ocean salinity, surface freshwater fluxes (precipitation and evaporation), and AMFT (RAPID array) at 26.5 degrees north latitude. Ta.

Changes in ocean freshwater content are influenced by surface freshwater fluxes and AMFT convergence. Therefore, AMFT can be calculated by subtracting the surface freshwater flux from the change in ocean freshwater content. Using this method, monthly AMFT was calculated over the range from 34°S to 66°N from 2004 to 2020.

The climatology, interannual variability, and trends of AMFT are analyzed based on the new estimates. Climatologically, the AMFT extends southward from 18°S to 34°S and northward from 18°S to 66°N.

On an interannual scale, AMFT shows clear variations in the regions from 34°S to 40°N and from 40°N to 66°N. These fluctuations may be due to changes in the drivers of AMFT in these regions.

Additionally, a notable finding from the new estimates is that, despite the relatively short time series, the AMFT showed a trend of increasing strength as it moves northward through different latitudes from 2004 to 2020.

However, the strength of this trend varies with latitude, resulting in both convergence and divergence regions in AMFT. These patterns of convergence and divergence influence the acceleration of changes in Atlantic freshwater content.

This method effectively addresses the limited observation range and provides valuable data for a deeper understanding of AMFT changes due to global warming.