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Palóczy, A, da Silveira ICA, Castro BM, Calado L.  2014.  Coastal upwelling off Cape São Tomé (22°S, Brazil): The supporting role of deep ocean processes. Continental Shelf Research. 89:38-50.   AbstractWebsite

The regional ocean off Cape São Tomé (CST, 22°S, Brazil) is known to feature transient coastal upwelling and intense mesoscale activity associated with the Brazil Current (BC). Satellite and in situ observations are used to characterize the coastal upwelling and the oceanic pycnocline water intrusions onto the continental shelf. Coastal upwelling events around CST are found to be less intense than the ones around Cape Frio (23°S), confirming previously reported findings. It is shown that the quasi-standing growth of a BC cyclonic meander is an effective supporting mechanism to this primarily wind-driven coastal upwelling system. A typical propagating cyclonic meander event is described and compared with its quasi-standing counterpart. The propagating cyclones also appear to promote oceanic pycnocline water intrusions, but at a lesser extent than the quasi-standing features. The supporting effect of the BC cyclones was quantified via simplified numerical experiments carried out with a 2D, primitive-equation numerical model. It is shown that meanders enhance intrusions as they grow, and may decrease by ≈50% the momentum input needed from the wind to cause coastal upwelling. Also, the role of the sloping of the isolines linked to the mean baroclinic structure of the Brazil Current is examined in idealized numerical experiments. This structure is shown to be sufficient to explain the observed time scales of coastal upwelling. The kind of meander-driven intrusion investigated here appears to be a regional singularity of the CST region, and may provide insight into the cross-shelf dynamics of other Western Boundary Current regions where similar quasi-standing instabilities exist.

Palóczy, A, Gille ST, McClean JL.  2018.  Oceanic heat delivery to the Antarctic continental shelf: Large‐scale, low‐frequency variability. Journal of Geophysical Research: Oceans.   10.1029/2018JC014345   AbstractWebsite

Onshore penetration of oceanic water across the Antarctic continental slope (ACS) plays a major role in global sea level rise by delivering heat to the Antarctic marginal seas, thus contributing to the basal melting of ice shelves. Here, the time‐mean (Φmean) and eddy (Φeddy) components of the heat transport (Φ) across the 1000 m isobath along the entire ACS are investigated using a 0.1° global coupled ocean/sea ice simulation based on the Los Alamos Parallel Ocean Program (POP) and sea ice (CICE) models. Comparison with in situ hydrography shows that the model successfully represents the basic water mass structure, with a warm bias in the Circumpolar Deep Water layer. Segments of on‐shelf Φ, with lengths of O(100‐1000 km), are found along the ACS. The circumpolar integral of the annually‐averaged Φ is O(20 TW), with Φeddy always on‐shelf, while Φmean fluctuates between on‐shelf and off‐shelf. Stirring along isoneutral surfaces is often the dominant process by which eddies transport heat across the ACS, but advection of heat by both mean flow‐topography interactions and eddies can also be significant depending on the along‐ and across‐slope location. The seasonal and interannual variability of the circumpolarly‐integrated Φmean is controlled by convergence of Ekman transport within the ACS. Prominent warming features at the bottom of the continental shelf (consistent with observed temperature trends) are found both during high‐SAM and high‐Niño 3.4 periods, suggesting that climate modes can modulate the heat transfer from the Southern Ocean to the ACS across the entire Antarctic margin.

Palóczy, A, Brink KH, da Silveira ICA, Arruda WZ, Martins RP.  2016.  Pathways and mechanisms of offshore water intrusions on the Espírito Santo Basin shelf (18°S–22°S, Brazil). Journal of Geophysical Research: Oceans. 121:5134–5163.   10.1002/2015JC011468   AbstractWebsite

The pathways and physical mechanisms associated with intrusions of cold, nutrient‐rich South Atlantic Central Water (SACW) on the continental shelf of the Espírito Santo Basin (ESB), off southeast Brazil (18°S–22°S), are investigated. To this end, a set of process‐oriented, Primitive‐Equation (PE) numerical models are used, together with an independent and more complete PE model, available observations and simple theoretical ideas. SACW enters the model ESB shelf mostly through two preferential pathways along the Tubarão Bight (TB, 19.5°S–22°S). These pathways are found to be locations where an equatorward along‐isobath pressure gradient force (PGFy*) of O(10-6 m s-2) develops in response to steady wind forcing. This equatorward PGFy* is essentially in geostrophic balance, inducing onshore flow across the shelf edge, and most of the shelf proper. The Brazil Current (BC) imparts an additional periodic (in the along‐shelf direction) PGFy* on the shelf. The intrinsic pycnocline uplifting effect of the BC in making colder water available at the shelf edge is quantified. The BC also induces local intrusions by inertially overshooting the shelf edge, consistent with estimated Rossby numbers of ~0.3–0.5. In addition, the planetary β‐effect is related to a background equatorward PGFy*. A modified Arrested Topographic Wave model is shown to be a plausible rationalization for the shelf‐wide spreading of the pressure field imparted by the BC at the shelf edge. The deep‐ocean processes examined here are found to enhance the onshore transport of SACW, while wind forcing is found to dominate it at leading order.