Abstract
Abstract. Marine ecosystems are increasingly stressed by human-induced changes. Marine ecosystem drivers that contribute to stressing ecosystems – including warming, acidification, deoxygenation and perturbations to biological productivity – can co-occur in space and time, but detecting their trends is complicated by the presence of noise associated with natural variability in the climate system. Here we use large initial-condition ensemble simulations with an Earth system model under a historical/RCP8.5 (representative concentration pathway 8.5) scenario over 1950–2100 to consider emergence characteristics for the four individual and combined drivers. Using a 1-standard-deviation (67% confidence) threshold of signal to noise to define emergence with a 30-year trend window, we show that ocean acidification emerges much earlier than other drivers, namely during the 20th century over most of the global ocean. For biological productivity, the anthropogenic signal does not emerge from the noise over most of the global ocean before the end of the 21st century. The early emergence pattern for sea surface temperature in low latitudes is reversed from that of subsurface oxygen inventories, where emergence occurs earlier in the Southern Ocean. For the combined multiple-driver field, 41% of the global ocean exhibits emergence for the 2005–2014 period, and 63% for the 2075–2084 period. The combined multiple-driver field reveals emergence patterns by the end of this century that are relatively high over much of the Southern Ocean, North Pacific, and Atlantic, but relatively low over the tropics and the South Pacific. For the case of two drivers, the tropics including habitats of coral reefs emerges earliest, with this driven by the joint effects of acidification and warming. It is precisely in the regions with pronounced emergence characteristics where marine ecosystems may be expected to be pushed outside of their comfort zone determined by the degree of natural background variability to which they are adapted. The results underscore the importance of sustained multi-decadal observing systems for monitoring multiple ecosystems drivers.
Highlights
An important priority in climate research is to understand the potential vulnerabilities of marine ecosystems in the face of anthropogenic climate change (e.g., Doney et al, 2012)
The subtropical sea surface temperature (SST) tends to emerge from the 67 % confidence interval by 1990–2010, with this not being the case for the Southern Ocean and the Northern subpolar/Arctic regions
The commonality is that arag is above the 67 % confidence interval in all regions for the duration of the analysis period, whereas the net primary productivity (NPP) signal remains below the 67 % confidence level for the duration of the analysis period in all regions, with the exception of the southern subtropics for the period post-2070
Summary
An important priority in climate research is to understand the potential vulnerabilities of marine ecosystems in the face of anthropogenic climate change (e.g., Doney et al, 2012). Multiple drivers of marine ecosystems such as ocean warming, ocean acidification, nutrient stress and low oxygen levels have been identified to be among those of greatest concern (e.g., Gruber, 2011; Hall et al, 2013). The oceanic response to these changes, namely the oceanic uptake of excess heat and anthropogenic CO2 causes ocean warming and ocean acidification, i.e., a decrease in both oceanic pH and in the saturation state of seawater with regard to mineral calcium carbonate (Doney et al, 2009). The warming of the ocean tends to stratify the upper ocean (Sarmiento et al, 1998), leading to a reduced supply of nutrients to the euphotic zone (Bopp et al, 2001; Steinacher et al, 2010), and to a reduced resupply of oxygen to the ocean’s
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