Synergistic effects of iron and temperature on Antarctic phytoplankton and microzooplankton assemblages

Abstract

Abstract. Iron availability and temperature are important limiting factors for the biota in many areas of the world ocean, and both have been predicted to change in future climate scenarios. However, the impacts of combined changes in these two key factors on microbial trophic dynamics and nutrient cycling are unknown. We examined the relative effects of iron addition (+1 nM) and increased temperature (+4 • C) on plankton assemblages of the Ross Sea, Antarctica, a region characterized by annual algal blooms and an active microbial community. Increased iron and temperature individually had consistently significant but relatively minor positive effects on total phytoplankton abundance, phytoplankton and microzooplankton community composition, as well as photosynthetic parameters and nutrient drawdown. Unexpectedly, increased iron had a consistently negative impact on microzooplankton abundance, most likely a secondary response to changes in phytoplankton community composition. When iron and temperature were increased in concert, the resulting interactive effects were greatly magnified. This synergy between iron and temperature increases would not have been predictable by examining the effects of each variable individually. Our results suggest the possibility that if iron availability increases under future climate regimes, the impacts of predicted temperature increases on plankton assemblages in polar regions could be significantly enhanced. Such synergistic and antagonistic interactions between individual climate change variables highlight the importance of multivariate studies for marine global change experiments.

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

“…Our findings imply that if, due to climate change, present habitats for larval krill overwintering and nursery in the South Scotia Ridge and southern Scotia Sea 1 become ice free in winter, there may be an increase in food for larval krill development and growth [32][33][34][35][36][37] . If, however, the seasonal sea-ice cover does not extend as far north in future, then larvae that are released from under the sea ice in spring will be farther south in the Weddell Sea (south of the South Scotia Ridge in spring) and will take longer to reach the Scotia Sea 17 ( Supplementary Fig.…”

Southern Ocean phytoplankton physiology in a changing climate

“…Studies of Antarctic phytoplankton indicate that a rise in temperature alone causes only a modest increase in their growth rate (e.g. Rose et al, 2009;Boyd et al, 2013Boyd et al, , 2015 and this increase is often overcompensated by the negative effects of increased temperature on abiotic and biotic stressors such as nutrient limitation and grazing (Caron and Hutchins, 2013;Lewandowska et al, 2014).…”

CHLOROPHYLL a BIOMASS AND ACCESSORY CHLOROPHYLL PIGMENTS IN THE SHALLOW COASTAL ZONE AT ADMIRALTY BAY, ANTARCTICA: COMPARISON BETWEEN TWO CONSECUTIVE AUSTRAL SUMMERS

“…In general, Chl a concentrations were low (1-2 µg L-1) in spite of high dissolved inorganic nutrients concentrations (Cascaes et al, 2012), as commonly reported in Admiralty Bay (Lipski, 1987;Lange et al, 2007;Kopczynska, 2008). One of the explanations for this paradox is usually associated to the low micronutrient iron availability, which is considered as one of the main factors limiting phytoplankton growth under high macronutrients conditions (Martin et al, 1991;Rose et al, 2009). Studies developed on Antarctic phytoplankton cultures showed that both iron addition and increase in water temperature, lead to rise of chlorophyll biomass (Rose et al, 2009).…”

“…One of the explanations for this paradox is usually associated to the low micronutrient iron availability, which is considered as one of the main factors limiting phytoplankton growth under high macronutrients conditions (Martin et al, 1991;Rose et al, 2009). Studies developed on Antarctic phytoplankton cultures showed that both iron addition and increase in water temperature, lead to rise of chlorophyll biomass (Rose et al, 2009). In this way, the increase of biomass in LS was mainly conditioned by rise of temperature, which melts the ice providing the micronutrient iron to phytoplankton growth (Martin et al, 1991).…”

“…The Chl a biomass is generally low in the Southern Ocean despite the presence of high macronutrient concentration (Martin et al, 1991;Rose et al, 2009). Research studies in Admiralty Bay since the 80's reported Chl a concentrations during summer periods usually below 1 µg L -1 (Kopczynska, 1980;Lipski, 1987;Lange et al, 2007).…”