Holocene variations in productivity associated with changes in glacier activity and freshwater flux in the central basin of the Strait of Magellan

Abstract

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.

Winter distribution of toxic, potentially toxic phytoplankton, and shellfish toxins in fjords and channels of the Aysen region, Chile

“…This is suggested by results reported for sectors of the Magellanes region, the southernmost region of Chile (e.g., Pizarro et al, 2011Pizarro et al, , 2015. This is an aspect, not yet been evaluated, that needs to be incorporated in the studies carried out since they have to do with the interannual variability observed in microalgae distribution, c) the effects of freshwater fronts, produced by existing river and glacier discharges acting as walls or barriers to containment and physical accumulation, probably affecting important biological aspects, such as physiology, and microalgae life cycles, especially for dinoflagellates, another aspect not been evaluated at the spatial mesoscale level, d) mixotrophic capacity of dinoflagellates, unlike diatoms, in environments with high levels of dissolved organic matter (autochthonous and allochthonous), especially during winter (Pizarro et al, 2005), characteristic of southern fjords, channels and embayments ecosystems of Chile, an aspect that has not been evaluated as a factor favoring dinoflagellates persistence during the winter period, as well as their influence on the proliferation of others dinoflagellates species that follow diatom summer blooms or events of high seasonal primary production (Aracena et al, 2011(Aracena et al, , 2015Paredes et al, 2014).…”

Carbon flow through the pelagic food web in southern Chilean Patagonia: relevance of Euphausia vallentini as a key species

“…Therefore, the freshwater supply into the local channels and fjords comes from rain, snow, runoff and glacier melting from the Darwin Mountain Range (see Fig. 1 from Aracena et al 2015 for a detailed distribution of the location of the Darwin Mountain Range and melt water flow).…”

Late Holocene intensification of the westerly winds at the subantarctic Auckland Islands (51° S), New Zealand

“…From ∼ 900 to 750 yr BP, roughly coincident with the end of the MCA (1000-700 yr BP; MassonDelmotte et al, 2013), the winds contracted further north and this was likely associated with dominance of the negative phase of the SAM during this time (Abram et al, 2014;Moreno et al, 2014;Villalba et al, 1997Villalba et al, , 2012. Comparison with records from 51 to 53 • S in southern South America (Aracena et al, 2015;Moreno et al, 2014;Moy et al, 2009;Schimpf et al, 2011;Turney et al, 2016b) and West Antarctica (Koffman et al, 2014;Shevenell et al, 2011) identifies a late Holocene intensification of the SHWW, indicating that the winds may have been zonally symmetric across the Pacific Ocean from at least 1600 to 900 yr BP, and asymmetric after this.…”

“…9), consistent with our record from the Auckland Islands. Another study from a fjord system in the Strait of Magellan (53 • S, 70 • W), southern Patagonia, reconstructs Holocene changes in westerly wind-derived precipitation and associated changes in salinity and productivity using accumulation rates of biogenic silica, organic carbon, biogenic carbonate, and siliciclastics (Aracena et al, 2015). Increased siliciclastic, organic carbon (both marine and terrestrial) and carbonate AR at ∼ 2 ka likely indicates an intensification of freshwater flux from increased precipitation (hence SHWW intensification) at this time.…”

“…Palaeoclimate records of wind strength reconstruct changes in atmospheric circulation using the strong positive correlation between wind strength and precipitation in the middle latitudes of the Southern Hemisphere (Garreaud, 2007). Although there are a number of records from southern New Zealand (Gellatly et al, 1988;Knudson et al, 2011;Lorrey et al, 2008Lorrey et al, , 2014Putnam et al, 2010;Turney et al, 2017), Tasmania (Saunders et al, 2012), and southern South America (Aracena et al, 2015;Ariztegui et al, 2010;Lamy et al, 2001Lamy et al, , 2010Moreno et al, 2009Moreno et al, , 2014Moy et al, 2008Moy et al, , 2009Schmipf et al, 2011;Turney et al, 2016a;Waldmann et al, 2010;and others), there are fewer from the subantarctic islands, all of which have a palaeovegetation focus (McFadgen and Yaldwyn, 1984;McGlone 2002;McGlone et al, 2000McGlone et al, , 2010McGlone and Moar, 1997;Turney et al, 2016b).…”