No abstract

No abstract

No abstract

Ecosystems damaged by distal volcanic ash and sulfur deposition usually recover within decades. However, sediment, stalagmite, and pollen records from the southernmost Andes indicate a 2000 yr impact on forest and aquatic ecosystems after deposition of a thin tephra layer. SO 2 released from altering pumice produced intense soil and lake acidification in a Ͼ150,000 km 2 area. Acidification led to nutrient leaching and affected soil microorganisms, causing plant decay and increased soil erosion in an area larger than 8000 km 2. We conclude that weakly buffered soils in humid environments are extremely vulnerable to volcanic and anthropogenic acidification, causing long-lasting ecosystem damage and perturbations of paleoclimate proxy records.

One of the most important factors controlling fjord primary production in southernmost Patagonia is the variability in the thermohaline structure of the water column. In the present-day environment, thermal stratification is mostly related to freshwater input and in particular, the seasonal melting of glaciers. Here we assess whether this relation between fjord productivity and freshwater input holds true for the Holocene, using a sediment record from the central basin of the Strait of Magellan (core MD07-3132, 53°44.17′S; 70°19.03′W, 301 m). Our approach relies on a proxy-based reconstruction of fjord sea surface temperature (alkenone SST), paleosalinity, freshwater input, and paleoproductivity. The results indicate that, during the early Holocene, the accumulation rate (AR) of marine organic carbon was low (b 20 kg m −2 kyr −1), most likely due to high freshwater contribution resulting in low salinity and low SSTs. After 8.5 kyr BP and during the mid and late Holocene all the productivity proxies increase. The AR's of marine organic carbon (~30 kg m −2 kyr ) reached the highest values during the last millennium. This increase was probably driven by the marine transgression where marine macronutrient-rich waters entered into the central basin, while lowered precipitation and decreased meltwater input contributed to increase the basin's SSTs and salinity. The late Holocene rise in productivity was interrupted by a low salinity phase between 3.2 and 2.2 kyr BP, during which productivity returned to early Holocene conditions in response to increased input of glacial clays, as suggested by high values of K/Si ratio (~1.2). Our results indicate that meltwater contribution from glaciers plays a crucial role in controlling fjord productivity on seasonal to millennial timescales.