Ocean circulation along the southern Chile transition region (38°–46°S): Mean, seasonal and interannual variability, with a focus on 2014–2016

Abstract

Satellite and atmospheric model fields are used to describe the wind forcing, surface ocean circulation, temperature and chlorophyll-a pigment concentrations along the coast of southern Chile in the transition region between 38° and 46°S. Located inshore of the bifurcation of the eastward South Pacific Current into the equatorward Humboldt and the poleward Cape Horn Currents, the region also includes the Chiloé Inner Sea and the northern extent of the complex system of fjords, islands and canals that stretch south from near 42°S. The high resolution satellite data reveal that equatorward currents next to the coast extend as far south as 48°−51°S in spring-summer. They also display detailed distributions of forcing from wind stress and wind stress curl near the coast and within the Inner Sea. Between 38°−46°S, both winds and surface currents during 1993–2016 change directions seasonally from equatorward during summer upwelling to poleward during winter downwelling, with cooler SST and greater surface chlorophyll-a concentrations next to the coast during upwelling, opposite conditions during downwelling. Over interannual time scales during 1993–2016, there is a strong correlation between equatorial El Niño events and sea level and a moderate correlation with alongshore currents. Looking more closely at the 2014–2016 period, we find a marginal El Niño during 2014 and a strong El Niño during 2015 that connect the region to the tropics through the oceanic pathway, with some atmospheric connections through the phenomenon of atmospheric blocking (as noted by others). The period also includes a Harmful Algal Bloom of the dinoflagellate Alexandrium catenella during early-2016 that occurred during a sequence of physical conditions (winds, currents and temperatures) that would favor such a bloom. The most anomalous physical condition during this specific bloom is an extreme case of atmospheric blocking that creates a long period of calm in austral autumn after strong upwelling in austral summer. The blocking is related to the 2015–2016 El Niño and an unusual coincident positive phase of the Southern Annular Mode.

Coupled Biospheric Synchrony of the Coastal Temperate Ecosystem in Northern Patagonia: A Remote Sensing Analysis

“…The area to the south of Desertores Islands (see Figure 1B) is colder than the northern area due to its direct connection with oceanic SST patterns, especially during the autumn and winter months. Strub et al [62] reports on strong topographic and hydrographic mixing around Desertores island, which we hypothesize can act as a spatial barrier to the various synchrony patterns observed in our analysis.…”

“…The frequency-dependence underscores the importance of considering different time scales [2,11,14]. The mechanisms for the different responses in frequency, chiefly persistent synchrony between primary production and SAM in the southern sector post-2010, could be attributed to the different cooling patterns around our study region [62]. The area to the south of Desertores Islands (see Figure 1B) is colder than the northern area due to its direct connection with oceanic SST patterns, especially during the autumn and winter months.…”

“…Variability over higher frequencies and the 2-year mode after 2011 appears to be linked to SAM, whereas more extended periods of oscillation, such as 2-3-year mode before 2011 and the 4-5 years mode appear to be associated mainly to SOI, while after 2011 SAM appears as an essential contributor over the same temporal scales. The higher biological activity in the northern area could be related to coastal topography and the presence of a cluster of smaller islands driving strong physical-biological coupling in the sector [16,24,62]. Iriarte et al [63] showed significant associations between autotrophic abundance and streamflow of the Puelo River, which drains in the central part of the northern sector.…”

Connections Between Benthic Populations and Local Strandings of the Southern Bull Kelp Durvillaea Antarctica Along the Continental Coast of Chile1

“…, Strub et al. ), some areas of coastal recess do exist (e.g., north/south of Concepción, Santo Domingo, Queule) and the regional topography on a small scale (tens of km) can be diverse.…”

Impacts of reduced inorganic N:P ratio on three distinct plankton communities in the Humboldt upwelling system

“…Upwelling off the Chilean coast takes place north of 38°S and extends seasonally down to 46°S (Strub et al 2019). Large chains of diatoms typically dominate during periods with strong upwelling, whereas picophytoplankton, nanoplankton, and dinoflagellates increase in importance during periods with less frequent or lower intensity upwelling (Anabalón et al 2007;Collado-Fabbri et al 2011;Anabalón et al 2016).…”