Abstract
Abstract. The seasonal cycle (i.e. phenology) of oceanic primary production (PP) is expected to change in response to climate warming. Here, we use output from 6 global biogeochemical models to examine the response in the seasonal amplitude of PP and timing of peak PP to the IPCC AR5 warming scenario. We also investigate whether trends in PP phenology may be more rapidly detectable than trends in annual mean PP. The seasonal amplitude of PP decreases by an average of 1–2% per year by 2100 in most biomes, with the exception of the Arctic which sees an increase of ~1% per year. This is accompanied by an advance in the timing of peak PP by ~0.5–1 months by 2100 over much of the globe, and particularly pronounced in the Arctic. These changes are driven by an increase in seasonal amplitude of sea surface temperature (where the maxima get hotter faster than the minima) and a decrease in the seasonal amplitude of the mixed layer depth and surface nitrate concentration. Our results indicate a transformation of currently strongly seasonal (bloom forming) regions, typically found at high latitudes, into weakly seasonal (non-bloom) regions, characteristic of contemporary subtropical conditions. On average, 36 yr of data are needed to detect a climate-change-driven trend in the seasonal amplitude of PP, compared to 32 yr for mean annual PP. Monthly resolution model output is found to be inadequate for resolving phenological changes. We conclude that analysis of phytoplankton seasonality is not necessarily a shortcut to detecting climate change impacts on ocean productivity.
Highlights
To coincide with the mean bloom start date (Koeller et al., 2al0s0o9i)m
We examine the possibility that global warming may be more readily detectable in phenological markers than in other metrics, using output from 6 biogeochemical models run for the IPCC Coupled Model Intercomparison Project Phase 5 (CMIP5) project (Taylor et al, 2012) to examine how the timing of peak production and the amplitude of the seasonal cycle respond to climate change up to the year 2100
A visual comparison shows that the models broadly reproduce the spatial patterns of the satellite-derived primary production (PP) in both the seasonal amplitude and timing of peak PP reasonably well www.biogeosciences.net/10/4357/2013/
Summary
To coincide with the mean bloom start date (Koeller et al., 2al0s0o9i)m. CphacatngoecseatonitcheTcsaherbaesoonnCeaxlriptyyoorotfsapnprdihmseatorryreapgreod(Lucuttizonetmaaly., 2007), as regions with large amplitude seasonal cycles, e.g. Deep winter mixing results in light limitation of phytoplankton growth but at the same time ensures a plentiful supply of nutrients, so that shoaling of the mixed layer in spring results in rapid, sustained growth, i.e. a strong seasonal cycle This is in contrast to subtropical regions where mixed layers are sufficiently shallow year-round such that light limitation does not occur. Even weaker (non-existent) seasonality is found in oligotrophic regions where persistent stratification leads to chronic nutrient limitation, and only small, sporadic increases in phytoplankton abundance occur, with no annual repeating cycle In this context, continued global warming, leading to increased stratification, is hypothesised to reduce the seasonal magnitude of ocean primary production in nutrient-limited regions, but may advance the phytoplankton growth season in light-limited regions (due to earlier alleviation of light limitation) and result in stronger blooms (Bopp et al, 2001; Doney, 2006). We investigate whether climate-change-driven trends are detectable more rapidly in PP seasonality than in PP itself
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