Mesoscale and wind-driven intra-annual variability in the East Auckland Current

Area of Science:

• Oceanography
• Physical Oceanography
• Marine Dynamics

Background:

• Intra-annual variability in ocean currents impacts marine ecosystems and climate.
• The East Auckland Current (EAuC) is a key feature of the region's ocean circulation.
• Understanding upper ocean dynamics is essential for coastal management and climate modeling.

Purpose of the Study:

• To investigate the intra-annual variability of the East Auckland Current (EAuC).
• To determine the influence of mesoscale eddies and wind forcing on EAuC dynamics.
• To analyze the relationship between current variability and environmental factors like temperature and salinity.

Main Methods:

• Utilized a year-long timeseries of in situ and satellite-derived velocity, temperature, and salinity data.
• Employed statistical analysis to correlate satellite and in situ velocity observations.
• Analyzed current variability in relation to wind stress and wind stress curl.

Main Results:

• Satellite-derived velocities accurately represented long-term upper ocean circulation variability.
• Four mesoscale eddies were identified, influencing flows between the continental slope and rise.
• The EAuC dominated circulation for 110 days, with energetic events linked to wind forcing.
• Current variability on the continental slope showed coherence with along-slope wind stress and wind stress curl at specific periods.
• Offshore Ekman transport, shelf-break uplift, and geostrophic jets were associated with along-slope winds.
• Positive wind stress curl led to water convergence, downwelling, and increased current speed.
• EAuC-generated bottom Ekman transport likely caused significant temperature anomalies at the shelf-break.

Conclusions:

• The EAuC plays a dominant role in regional ocean circulation, particularly at the shelf break and slope.
• Wind forcing, including wind stress and wind stress curl, significantly drives EAuC variability and associated phenomena like Ekman transport.
• Mesoscale eddies contribute to the complex flow patterns in the study area.
• The findings enhance our understanding of upper ocean dynamics and their drivers in this region.