Abstract
This study investigates the mechanisms that control the occurrence of cold water intrusion events observed in Guanabara Bay, Rio de Janeiro, Brazil. To achieve this, we used multiple time-series data comprising in-situ temperatures recorded at depths of 5 m and 20 m in three sites in the Guanabara Bay region, wind velocities from three meteorological stations along the Brazilian coast, and sea level data from a tidal gauge located in the interior of Guanabara Bay. We found that from October 2014 to May 2016, near-bed temperatures in Guanabara Bay were dominated by subinertial variability. We identified subinertial cold water events, defined by temperature values below 18 °C, that were associated with South Atlantic Central Water intrusions. We obtained a total of 21 cold water events during the 18-month (545-day) sampling period, corresponding to 92.5 days or 17% of the time. Additionally, we found statistically significant lag-adjusted correlation coefficients (0.37-0.95) between near-bed (20 m) temperatures in Guanabara Bay and alongshore winds from the Arraial do Cabo meteorological station, which act in the well-known Cabo Frio upwelling system along the coast. These upwelling-favorable winds led near-bed temperature values in Guanabara Bay by 12 to 56 h and provided the remote forcing mechanism for the cold water intrusions in Guanabara Bay. Locally, the shelf-bay intrusion velocity values ranged from 0.04 to 0.50 ms−1, consistent with a gravity current enhanced by baroclinic pressure gradient, the local forcing mechanism. The cold water intrusions caused an increase in the vertical temperature stratification within Guanabara Bay, as verified for all analyzed events. We also identified subinertial oscillations due to Coastal Trapped Waves (CTWs) propagation from our sea level data records and evaluated their impacts on cold water events.
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