To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the Oceanography Society and can be found at: http://www.tos.org/oceanography/index.html.The goal of the Pacific Ocean Boundary Ecosystem and Climate Study\ud (POBEX) was to diagnose the large-scale climate controls on regional transport\ud dynamics and lower trophic marine ecosystem variability in Pacific Ocean boundary\ud systems. An international team of collaborators shared observational and eddy-resolving\ud modeling data sets collected in the Northeast Pacific, including the Gulf of\ud Alaska (GOA) and the California Current System (CCS), the Humboldt or Peru-Chile\ud Current System (PCCS), and the Kuroshio-Oyashio Extension (KOE) region. POBEX\ud investigators found that a dominant fraction of decadal variability in basin- and\ud regional-scale salinity, nutrients, chlorophyll, and zooplankton taxa is explained by a\ud newly discovered pattern of ocean-climate variability dubbed the North Pacific Gyre\ud Oscillation (NPGO) and the Pacific Decadal Oscillation (PDO). NPGO dynamics\ud are driven by atmospheric variability in the North Pacific and capture the decadal\ud expression of Central Pacific El Niños in the extratropics, much as the PDO captures\ud the low-frequency expression of eastern Pacific El Niños. By combining hindcasts\ud of eddy-resolving ocean models over the period 1950–2008 with model passive\ud tracers and long-term observations (e.g., CalCOFI, Line-P, Newport Hydrographic\ud Line, Odate Collection), POBEX showed that the PDO and the NPGO combine to\ud control low-frequency upwelling and alongshore transport dynamics in the North\ud Pacific sector, while the eastern Pacific El Niño dominates in the South Pacific.\ud Although different climate modes have different regional expressions, changes in\ud vertical transport (e.g., upwelling) were found to explain the dominant nutrient and\ud phytoplankton variability in the CCS, GOA, and PCCS, while changes in alongshore\ud transport forced much of the observed long-term change in zooplankton species\ud composition in the KOE as well as in the northern and southern CCS. In contrast,\ud cross-shelf transport dynamics were linked to mesoscale eddy activity, driven by\ud regional-scale dynamics that are largely decoupled from variations associated with\ud the large-scale climate modes. Preliminary findings suggest that mesoscale eddies\ud play a key role in offshore transport of zooplankton and impact the life cycles of\ud higher trophic levels (e.g., fish) in the CCS, PCCS, and GOA. Looking forward,\ud POBEX results may guide the development of new modeling and observational\ud strategies to establish mechanistic links among climate forcing, mesoscale circulation,\ud and marine population dynamics

This article presents the results of a high‐resolution (1/12°), two‐way nested simulation of the oceanic circulation in the southwestern Atlantic region. A comparison between the model results and extant observations indicates that the nested model has skill in reproducing the best‐known aspects of the regional circulation, e.g., the volume transport of the ACC, the latitudinal position of the BMC, the shelf break upwelling of Patagonia, and the Zapiola Anticyclone. Sensitivity experiments indicate that the bottom stress parameterization significantly impacts the mean location of the Brazil/Malvinas Confluence and the transport of the Zapiola Anticyclone. The transport of the Brazil Current strengthens during the austral summer and weakens during the austral winter. These variations are driven by the wind stress curl over the southwestern Atlantic. The variations of the transport of the Malvinas Current are out of phase with those of the Brazil Current. Most of the seasonal variability of this current is concentrated in the offshore portion of the jet, the inshore portion has a weak seasonality that modulates the magnitude of the Patagonian shelf break upwelling. Using passive tracers we show that most of the entrainment of deep waters into the shelf occurs in the southernmost portion of the Patagonian shelf and along the inshore boundary of the Brazil Current. Shelf waters are preferentially detrained near the Brazil/Malvinas Confluence. Consistent with previous studies, our simulation also shows that south of ∼42°S the Malvinas Current is composed of two jets, which merge near 42°S to form a single jet farther north.

A high-resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal and the interannual variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA), the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high-frequency component of the wind stress forcing controls the vertical structure of the plumes while the low-frequency component of the wind stress forcing and the interannual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross-shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.