The variability of El Niño/Southern Oscillation (ENSO) during the Holocene epoch, in particular on millennial timescales, is poorly understood. Palaeoclimate studies have documented ENSO variability for selected intervals in the Holocene, but most records are either too short or insufficiently resolved to investigate variability on millennial scales. Here we present a record of sedimentation in Laguna Pallcacocha, southern Ecuador, which is strongly influenced by ENSO variability, and covers the past 12,000 years continuously. We find that changes on a timescale of 2-8 years, which we attribute to warm ENSO events, become more frequent over the Holocene until about 1,200 years ago, and then decline towards the present. Periods of relatively high and low ENSO activity, alternating at a timescale of about 2,000 years, are superimposed on this long-term trend. We attribute the long-term trend to orbitally induced changes in insolation, and suggest internal ENSO dynamics as a possible cause of the millennial variability. However, the millennial oscillation will need to be confirmed in other ENSO proxy records.
Iron is an essential micronutrient that limits primary productivity in much of the ocean, including the Gulf of Alaska (GoA). However, the processes that transport iron to the ocean surface are poorly quantified. We combine satellite and meteorological data to provide the first description of widespread dust transport from coastal Alaska into the GoA. Dust is frequently transported from glacially‐derived sediment at the mouths of several rivers, the most prominent of which is the Copper River. These dust events occur most frequently in autumn, when coastal river levels are low and riverbed sediments are exposed. The dust plumes are transported several hundred kilometers beyond the continental shelf into iron‐limited waters. We estimate the mass of dust transported from the Copper River valley during one 2006 dust event to be between 25–80 ktons. Based on conservative estimates, this equates to a soluble iron loading of 30–200 tons. We suggest the soluble Fe flux from dust originating in glaciofluvial sediment deposits from the entire GoA coastline is two to three times larger, and is comparable to the annual Fe flux to GoA surface waters from eddies of coastal origin. Given that glaciers are retreating in the coastal GoA region and in other locations, it is important to examine whether fluxes of dust are increasing from glacierized landscapes to the ocean, and to assess the impact of associated Fe on marine ecosystems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.