Wind-Driven Seasonal Intrusion of Modified Circumpolar Deep Water Onto the Continental Shelf in Prydz Bay, East Antarctica

Intrusion of warm modified Circumpolar Deep Water (mCDW) is critical to heat transport onto the continental shelf around Antarctica, with substantial impacts on basal melting of ice shelves and sea ice production. We use hydrographic data collected in Prydz Bay, East Antarctica, and atmospheric and ocean reanalyses to investigate the seasonality of mCDW intrusions onto the East Antarctic continental shelf. Mooring measurements confirm that there is significant intrusion of mCDW over the inner continental shelf of Prydz Bay in March-July (austral autumn and early winter). The warming signal of intruded mCDW over the inner shelf is correlated with wind changes north of the shelf break, with a significant lag. This suggests that the autumn-winter mCDW intrusions over the inner shelf are significantly affected by the wind regime north of the shelf break in January-May, when a southward displacement of the westerly winds occurs. The southward shift of westerly winds drives the shallowest depth of upwelled mCDW to move poleward and contributes more warm water to the shelf break. This results in the shoaling of mCDW near the shelf break in January-May and promotes mCDW intrusions onto the continental shelf. The dynamic barrier imposed on mCDW intrusions by the strong Antarctic Slope Front in January-May is offset by this shoaling of mCDW. This study indicates the strong sensitivity of continental shelves in East Antarctica to atmospheric forcing changes over the Southern Ocean. Plain Language Summary Warm modified Circumpolar Deep Water (mCDW) from the Southern Ocean flows onto the continental shelf in many regions around Antarctica. These intrusions transport great amounts of heat to the continental shelves, affecting basal melting of ice shelves and sea ice formation. Data collected over the continental shelf of Prydz Bay, East Antarctica show that these intrusions occur seasonally. When we combine these observations with results from atmospheric model, we find that the strongest intrusion of mCDW over the inner shelf in March-July is related to the variability of westerly winds north of the shelf break in January-May. This is the period when the westerly winds over the Southern Ocean move southward. This causes the mCDW to become shallower near the shelf break and allows more warm water to flow to the inner shelf. Although an intensified Antarctic Slope Front in January-May should block the intrusion of mCDW, the blocking effect is overwhelmed by the shallowing of mCDW. Our findings provide insights into how seasonal variability of atmospheric forcing in the open ocean will affect warm water inflow and heat transport onto continental shelves in East Antarctica, and indicate potential effects of future changes in winds around Antarctica.