CRP El Niño member - Mr. Dimitri Gutierrez
Mr. Dimitri Gutierrez
Instituto del Mar del Peru
The Peruvian Coastal Upwelling Ecosystem is complex, variable and productive, being subjected to significant interannual variability as a consequence of the El Niño Southern Oscillation cycle (ENSO), and its warm and cold phases named El Niño (EN) and La Niña (LN). Among the main oceanographic and ecological features off the Peruvian coast during neutral and cold ENSO conditions, it should be mentioned here:
- a rather permanent coastal upwelling due to the action of the southeastern trade winds
- a shallow but intense oxygen minimum zone (OMZ, < 0.5 ml L-1, ~ 50-500 m) that intersects the coastal margin and affects the biological communities and biogeochemical processes in the water column and in the sediments
- a dominant poleward circulation near the coast, consisting in a shallow inshore (< 100 km), equatorward wind-drift current and a poleward undercurrent (PUC) associated to the core of the OMZ
- Primary production rates reaching 1 kg C m-2 y-1 on average in upwelling waters. These conditions make unlikely the developmentof coral populations in the ecosystem domain, but enable the upper continental margin sediments to record the environmental and ecosystem variability, due to the combination of high productivity, near-anoxic conditions over the bottom and low dilution by terrigenous sediments in certain areas (Krissek & Scheidegger, 1983; Suess et al., 1990).
A major part of the upper continental margin sediments are characterized by very high contents of organic matter in the surface layers. Fine sediments and organic carbon content tend to increase from north to south, in a rough parallelism with the latitudinal trend of the vertical and horizontal extension of the OMZ. On the other hand, the continental shelf is wider (up to 80 miles) off the northern and central coast (north of 14ºS), while it almost dissappears off the southern coast. Therefore the central Peruvian continental margin appears as a region of enhanced sedimentation and burial of organic carbon. There are observed several nuclei of very high surface organic carbon content (> 10%) below upwelling centers in wide shelf areas (Delgado & Gomero, 1988). Off the central coast (09-15° S), 210Pb-sedimentation rates vary from 0.05 cm y-1 to >0.2 cm y-1 on the continental shelf, and from 0.04 to 0.15 cm y-1 on the continental slope (Reimers & Suess, 1983; Henrichs & Farrington, 1984, McCaffrey et al., 1990, Levin et al., 2002, 2003, D. Gutiérrez & J.L. Reyss, unpub. data). In contrast, sediments of the Peru slope tend to be highly heterogeneous; authigenic precipitation of phosphorites, erosive processes and lateral transport are dominant processes superceding effects of depth or bottom water oxygenation on sediment properties (Levin et al., 2002).
A few studies have tried to reconstruct the recent decadal or subdecadal variability (from Holocene to past hundred of years) of the PCUE from the anoxic sediment records (e.g. McCaffrey et al., 1990, Skilbeck et al., 2004). Research studies from the ODP program have focused on longer time scales, though have revealed potential sites for higher resolution studies. In general, surface laminated sediments are present only in certain areas off the central coast, which implies a dedicated exploration effort to locate and map these spots.
In this context, the Instituto del Mar del Peru have started a research paleo-oceanographic program in 2003 with the general goal of reconstructing the past 2000 years of environmental (temperature, oxygen minimum) and ecosystem (productivity, ecosystem structure and fish population dynamics) variability of the PCUE. This program is complemented by collaborative projects with IRD-France (research unit Paleotropique) and other institutions from Latin America. Our research is focused on to locate the spots of laminated sediments, to characterize its background properties (sediment accumulation rates and sedimentological parameters) and to use a multiproxy approach (stable isotopic analyses of organic matter and foraminiferal tests, geochemical biomarkers, microfossil assemblages including fish scales) in order to reveal the past environmental and ecosystem variability. One of the specific goals is to precise if the sediment cores (or part of them) are able to record ENSO impacts (physico-chemical, geochemical, biological) and then permit to reconstruct this variability mode in the recent past.
Our participation in the CRP project Nuclear and isotopic studies of the El Niño phenomenon in the ocean will permit us to complement analytical tasks and to develop interactions with similar international research programs, which will enrich our current research goals and scopes. On the other hand, we expect to provide research products that will be of interest for our CRP research partners. Since we also are interested in develop a capacity building in Peruvian institutions (as Instituto del Mar del Perú and Instituto Peruano de Energía Nuclar) in order to sustain this sort of research in the future, we also expect to receive assistance to enhance the current facilities and personnel capabilities for paleoclimate research in Peru.