Hydrographic characteristics along two XCTD sections between Africa and Antarctica during austral summer 2018

• Published in: Polar Science
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Southern ocean; Hydrological fronts; Baroclinic transport; Water mass; Chlorophyll-a; Southern Ocean; Austral; Prydz Bay; Indian; Antarc*; Antarctica; Polar Science
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=16872; http://id.nii.ac.jp/1291/00016742/

Using the Expendable CTDs (XCTDs) collected along two transects between Africa and Antarctica during 1–11 January (Cape Town−Prydz Bay, track-2) and 12-21 April 2018 (Prydz Bay−Cape Town, track-1), frontal locations are delineated and compared with the satellite-based maps of absolute dynamic topography (MADT). The MADT maps revealed that the intensity of the Agulhas Current (AC) was 1.3 ms−1 during both periods; the southernmost limit of the Agulhas Retroflection (AR) was traced to 40°S, 20.5°E/42°S, 15°E on track-1/track-2. The vertical sections of temperature and salinity revealed the Agulhas anticyclonic eddy (AAE) whose core was detected at ~38.4°S/~37.6°S on track-1/track-2. The cumulative transport across track-2 was 50% higher than across track-1 which is attributed to deep-sea upwelling and its subsequent transport across the track-2 to the south of 50°S. On both transects, the winter water was detected up to 50°S in the upper 100 m. The highest AC transport in the upper 1000 m was detected at 37.75°S/38.28°S on track-1/track-2, which was related to the flow characteristics of the AC. The eddies that detached from the AC system transported nutrient-rich water southward which mixed with the ambient water resulting in peak chlorophyll-a concentration (Chl-a) exceeding 0.5 mg/m3 to the north of 42°S on both tracks. The shallow topographic features such as the Ob-Lena rise (54°S) and the southwest Indian Ridge (44°−46°S) also enhanced Chl-a by 39% on track-2.