Hypoxia in future climates: A model ensemble study for the Baltic Sea

Abstract

[1] Using an ensemble of coupled physical-biogeochemical models driven with regionalized data from global climate simulations we are able to quantify the influence of changing climate upon oxygen conditions in one of the numerous coastal seas (the Baltic Sea) that suffers worldwide from eutrophication and from expanding hypoxic zones. Applying various nutrient load scenarios we show that under the impact of warming climate hypoxic and anoxic areas will very likely increase or at best only slightly decrease (in case of optimistic nutrient load reductions) compared to present conditions, regardless of the used global model and climate scenario. The projected decreased oxygen concentrations are caused by (1) enlarged nutrient loads due to increased runoff, (2) reduced oxygen flux from the atmosphere to the ocean due to increased temperature, and (3) intensified internal nutrient cycling. In future climate a similar expansion of hypoxia as projected for the Baltic Sea can be expected also for other coastal oceans worldwide. Citation: Meier,

Extremes of Temperature, Oxygen and Blooms in the Baltic Sea in a Changing Climate

“…Salinity shows a clear decreasing tendency in accordance with Meier (2006), Neumann (2010), and Meier et al (2011c). The magnitude of the change should still be considered as relatively uncertain due to the uncertainty of precipitation in GCMs .…”

“…Oxygen conditions in general could deteriorate due to climate warming (Meier et al 2011c), due to decreasing solubility of oxygen in water with increasing temperature, and an acceleration of temperature-dependent degradation processes (Conley et al 2009). We found that the probability for hypoxic and anoxic conditions in the future projections increased in most bottom waters of the central Baltic Sea, and the maximum duration of hypoxic and anoxic events roughly doubled.…”

“…A multi-model ensemble simulation has been performed to assess the Baltic Sea ecosystem status in a future climate (Meier et al 2011c). Each of these experiments in the ensemble is subject to a specific evolution in time, depending on the future climate projection (IPCC scenario) and the models that are used.…”

“…For this study, we use a subset of the model experiments described in Meier et al (2011c) based on the IPCC A1B (IPCC 2007(IPCC , 2009) greenhouse gas emission scenario. The IPCC scenario was realized by the global circulation models ECHAM5 (Roeckner et al 2006) and HadCM3 (Gordon et al 2000).…”

“…2011a) and extended hypoxic areas (Meier et al 2011c). One objective of the Baltic Sea Action Plan (BSAP; HELCOM 2011) is the improvement of the oxygen conditions in the Baltic Sea deep water to be achieved by a reduction of riverine nutrient loads.…”