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Observations from a ship-based campaign in July-August 2009, combined with idealized numerical simulations, are used to investigate the seasonal delivery of Pacific Winter Water to Barrow Canyon and the subsequent adjustment of the flow down the canyon. As the current advects dense water, it transitions from a nearly barotropic structure near the canyon head to a strongly baroclinic flow with a subsurface maximum near the canyon mouth. Both the data and model indicate that the transit times along the three Chukchi Shelf pathways feeding Barrow Canyon – a coastal pathway, a southern Hanna Shoal pathway, and a northern Hanna Shoal pathway – modulate the mode of winter water that occupies the canyon at a given time. In particular, remnant Pacific Winter Water carried along the rapid coastal pathway can precede the arrival of newly ventilated Pacific Winter Water carried along the two interior pathways. The observations and model indicate that the transition between water types draining from the canyon can occur rapidly over time scales of days to weeks. We also demonstrate that mixing along the path of the current is unlikely to result in the observed down-canyon transition from newly ventilated Pacific Winter Water to remnant winter water, further supporting the dominant role of advection. While the focus here is on the transition of winter water modes, the implication that seasonality within Barrow Canyon is tied to seasonality of the Bering Strait inflow, together with the relative transit times along advective pathways, should hold for other water types as well. [ABSTRACT FROM AUTHOR]

The Bay of Bengal is forced by the South Asian monsoon and associated seasonally reversing winds and freshwater fluxes. Here, we summarize a high-resolution, basin-wide survey of the Bay of Bengal conducted during the 2013 northeast (winter) monsoon. The observed mixed layer waters were sourced from the eastern Bay; and, generally, the upper ocean temperature-salinity properties followed regional trends as determined by Argo. Intense lateral mixed layer gradients were seen throughout the Bay. The majority of the observed fronts were salinity-controlled with compensating temperature gradients. Similarly, salinity was typically the primary control on the vertical density stratification near the mixed layer depth. In contrast to the shallow, sharp halocline, temperature stratification was enhanced over a larger depth range with the base of the near-surface isothermal layer often located beneath the mixed layer, indicating the presence of a barrier layer. Finescale layers in vertical temperature and salinity stratification were traced over distances greater than 100 km in the horizontal. Within a ~ week-long period, we observed a significant reduction in the intensity of gradients (both lateral and vertical) as well as a shift in the relative importance of salinity in setting the observed gradients. By the end of the 17-day cruise when the ship was in the southern Bay of Bengal, temperature was an equal or dominant contributor to lateral and vertical gradients. Stratification and mixed layer fronts evolved over a relatively short time scale, likely in response to strong atmospheric forcing either associated with a tropical cyclone, sustained northeast monsoon conditions, or a combination of the two. Resolution of the observed lateral gradients requires sampling at lateral scales O (1 km) or smaller, suggestive of the importance of the submesoscale. [ABSTRACT FROM AUTHOR]

Located in the southwest Bay of Bengal, the Sri Lanka Dome (SLD) is an upwelling tropical thermal dome that forms in a region of positive wind stress curl within the Southwest Monsoon Current (SMC) system. Here, we quantify variability in the SLD's sea surface slope, area, amplitude, and position using a 22-year record of absolute dynamic topography. We observe a seasonal cycle in the evolution of the SLD and its relationship to wind stress curl. The SLD typically forms in early June in a region of positive wind stress curl associated with the wind jet off Sri Lanka. For the first two months after formation, the magnitude of the SLD's sea surface slope strongly correlates with the strength of the wind stress curl. Later in the southwest monsoon, the SLD's position shifts northward moving out of the region of strong wind stress curl, before dissipating in typically September. The amplitude and area of the SLD vary together, and both are linked to the strength of the SMC on weekly timescales. Decadal variability in both the SLD and wind stress curl is reflected in the Dipole Mode Index, which reflects an integrated measure of regional forcing. These results suggest alignment between the SMC and the region of wind stress curl may play a pivotal role in controlling the strength of the SLD on seasonal and interannual timescales. • We quantify the seasonal and interannual variability in the remotely sensed properties of Sri Lanka Dome (SLD). • The SLD forms early June in a region of positive wind stress curl then migrates north over the season away from that region. • Wind stress curl correlates with the meridional position and strength of the SLD during the first half of the SLD's lifespan. • The Dipole Mode Index relates to both wind stress curl and SLD strength and may explain observed decadal signals. [ABSTRACT FROM AUTHOR]