Detection of anthropogenic climate change in satellite records of ocean chlorophyll and productivity (original) (raw)
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Global patterns of change and variation in sea surface temperature and chlorophyll a
Scientific reports, 2018
Changes over the scale of decades in oceanic environments present a range of challenges for management and utilisation of ocean resources. Here we investigate sources of global temporal variation in Sea Surface Temperature (SST) and Ocean Colour (Chl-a) and their co-variation, over a 14 year period using statistical methodologies that partition sources of variation into inter-annual and annual components and explicitly account for daily auto-correlation. The variation in SST shows bands of increasing variability with increasing latitude, while the analysis of annual variability in Chl-a shows mostly mid-latitude high variability bands. Covariation patterns of SST and Chl-a suggests several different mechanisms impacting Chl-a change and variance. Our high spatial resolution analysis indicates these are likely to be operating at relatively small spatial scales. There are large regions showing warming and rising of Chl-a, contrasting with regions that show warming and decreasing Chl-a...
Remote Sensing
Primary production by marine phytoplankton is one of the largest fluxes of carbon on our planet. In the past few decades, considerable progress has been made in estimating global primary production at high spatial and temporal scales by combining in situ measurements of primary production with remote-sensing observations of phytoplankton biomass. One of the major challenges in this approach lies in the assignment of the appropriate model parameters that define the photosynthetic response of phytoplankton to the light field. In the present study, a global database of in situ measurements of photosynthesis versus irradiance (P-I) parameters and a 20-year record of climate quality satellite observations were used to assess global primary production and its variability with seasons and locations as well as between years. In addition, the sensitivity of the computed primary production to potential changes in the photosynthetic response of phytoplankton cells under changing environmental ...
Journal Of Geophysical Research: Oceans, 2014
Quantifying change in ocean biology using satellites is a major scientific objective. We document trends globally for the period 1998-2012 by integrating three diverse methodologies: ocean color data from multiple satellites, bias correction methods based on in situ data, and data assimilation to provide a consistent and complete global representation free of sampling biases. The results indicated no significant trend in global pelagic ocean chlorophyll over the 15 year data record. These results were consistent with previous findings that were based on the first 6 years and first 10 years of the SeaWiFS mission. However, all of the Northern Hemisphere basins (north of 10 latitude), as well as the Equatorial Indian basin, exhibited significant declines in chlorophyll. Trend maps showed the local trends and their change in percent per year. These trend maps were compared with several other previous efforts using only a single sensor (SeaWiFS) and more limited time series, showing remarkable consistency. These results suggested the present effort provides a path forward to quantifying global ocean trends using multiple satellite missions, which is essential if we are to understand the state, variability, and possible changes in the global oceans over longer time scales.
Response of ocean ecosystems to climate warming
Global Biogeochemical Cycles, 2004
1] We examine six different coupled climate model simulations to determine the ocean biological response to climate warming between the beginning of the industrial revolution and 2050. We use vertical velocity, maximum winter mixed layer depth, and sea ice cover to define six biomes. Climate warming leads to a contraction of the highly productive marginal sea ice biome by 42% in the Northern Hemisphere and 17% in the Southern Hemisphere, and leads to an expansion of the low productivity permanently stratified subtropical gyre biome by 4.0% in the Northern Hemisphere and 9.4% in the Southern Hemisphere. In between these, the subpolar gyre biome expands by 16% in the Northern Hemisphere and 7% in the Southern Hemisphere, and the seasonally stratified subtropical gyre contracts by 11% in both hemispheres. The low-latitude (mostly coastal) upwelling biome area changes only modestly. Vertical stratification increases, which would be expected to decrease nutrient supply everywhere, but increase the growing season length in high latitudes. We use satellite ocean color and climatological observations to develop an empirical model for predicting chlorophyll from the physical properties of the global warming simulations. Four features stand out in the response to global warming: (1) a drop in chlorophyll in the North Pacific due primarily to retreat of the marginal sea ice biome, (2) a tendency toward an increase in chlorophyll in the North Atlantic due to a complex combination of factors, (3) an increase in chlorophyll in the Southern Ocean due primarily to the retreat of and changes at the northern boundary of the marginal sea ice zone, and (4) a tendency toward a decrease in chlorophyll adjacent to the Antarctic continent due primarily to freshening within the marginal sea ice zone. We use three different primary production algorithms to estimate the response of primary production to climate warming based on our estimated chlorophyll concentrations. The three algorithms give a global increase in primary production of 0.7% at the low end to 8.1% at the high end, with very large regional differences. The main cause of both the response to warming and the variation between algorithms is the temperature sensitivity of the primary production algorithms. We also show results for the period between the industrial revolution and 2050 and 2090.
Variability of Large Marine Ecosystems in response to global climate change
2007
A fifty year time series of sea surface temperature (SST) and time series on fishery yields are examined for emergent patterns relative to climate change. More recent SeaWiFS derived chlorophyll and primary productivity data were also included in the examination. Of the 64 LMEs examined, 61 showed an emergent pattern of SST increases from 1957 to 2006, ranging from mean annual values of 0.08°C to 1.35°C. The rate of surface warming in LMEs from 1957 to 2006 is 4 to 8 times greater than the recent estimate of the Japan Meteorological Society’s COBE estimate for the world oceans. Effects of SST warming on fisheries, climate change, and trophic cascading are examined. Concern is expressed on the possible effects of surface layer warming in relation to thermocline formation and possible inhibition of vertical nutrient mixing within the water column in relation to bottom up effects of chlorophyll and primary productivity on global fisheries resources. 1. Background Large Marine Ecosystem...
Declining ocean chlorophyll under unabated anthropogenic CO 2 emissions
Environmental Research Letters, 2011
Photosynthetic assimilation of carbon dioxide and inorganic nutrients by phytoplankton constitutes a necessary prerequisite for sustaining marine life. This process is tightly linked to the concentration of chlorophyll in the ocean's euphotic zone. According to a recent field study marine chlorophyll(a) concentrations have declined over the last century with an estimated global rate of 1.0% of the global median per year. Here we attempt to identify possible mechanisms which could explain such trends. We explore these questions using an ocean general circulation model forced with documented historic and projected future anthropogenic emissions of carbon dioxide according to the IPCC SRES A1FI emission scenario until the year 2100. We further extend the time period covered by the A1FI scenario by assuming a linear decline in emissions from 2100 to 2200 and keeping them at zero levels until 2400. Our numerical simulations reveal only weak reductions in chlorophyll(a) concentrations during the twentieth century, but project a 50% decline between 2000 and 2200. We identify a local and a remotely acting mechanism for this reduction in the North Atlantic: (I) increased sea surface temperatures reduce local deep mixing and, hence, reduce the nutrient supply from waters at intermediate depths; (II) a steady shoaling of the Atlantic overturning cell tends to transport increasingly nutrient depleted waters from the Southern Hemisphere toward the north, leading to further diminishment of nutrient supply. These results provide support for a temperature-driven decline in ocean chlorophyll(a) and productivity, but suggest that additional mechanisms need to be invoked to explain observed declines in recent decades.
Global Biogeochemical Cycles, 2015
In this study we analyze large-scale satellite-derived data using generalized additive models to characterize the global correlation patterns between environmental forcing and marine phytoplankton biomass. We found systematic differences in the relationships between key environmental drivers (temperature, light, and wind) and ocean chlorophyll in the subtropical/tropical and temperate oceans. For the subtropical/tropical and equatorial oceans, the chlorophyll generally declined with increasing temperature and light, while in temperate oceans, chlorophyll was best explained by bell-shaped or positive functions of temperature and light. The relationship between chlorophyll and wind speed is generally positive in low-latitude oceans and bell shaped in temperate oceans. Our analyses also demonstrated strong and geographically consistent positive autoregressive effects of chlorophyll from 1 month to the next and negative autoregressive effects for measurements 2 months apart. These findings imply possibly different regional phytoplankton responses to environmental forcing, suggesting that future environmental change could affect the tropical and temperate upper ocean chlorophyll levels differently. Being unicellular, fast growing, and short lived, phytoplankton responds rapidly to external ambient drivers and environmental change [Hays et al., 2005]. Environmental forcings such as temperature, light, and wind speed are recognized as important physical factors affecting the dynamics of marine phytoplankton both directly and indirectly (e.g., via mixing regimes, nutrient dynamics, and grazing) [Chavez et al., 2011; Mauri et al., 2007], and these environmental drivers will vary among regions. For example, it has been suggested that there is a negative correlation between sea surface temperature (SST) and phytoplankton abundance in warm regions of Northeast Atlantic [Richardson and Schoeman, 2004] as well as Atlantic and Pacific gyres [Gregg et al., 2005]. Positive or nonlinear effects of temperature on phytoplankton have also been found in the North Sea [Llope et al., 2009] and cold regions of North Atlantic [Irwin and Finkel, 2008; Raitsos et al., 2006]. Sarmiento et al. [2004] evaluated environmental effects on annual chlorophyll using a linear regression model and found that these coefficients varied across ocean regions. Both positive and negative correlations have been reported between wind speed and chlorophyll concentration in different ocean regions [Kahru et al., 2010]. Given the possibly complex relationships between different environmental factors and ocean chlorophyll in different regions, it is a challenge to outline the general correlation patterns between them on a global scale.
Global ocean primary production trends in the modern ocean color satellite record (1998–2015)
Environmental Research Letters, 2019
Ocean primary production (PP), representing the uptake of inorganic carbon through photosynthesis, supports marine life and affects carbon exchange with the atmosphere. It is difficult to ascertain its magnitude, variability, and trends due to our inability to measure it directly at large scales. Yet it is paramount for understanding changes in marine health, fisheries, and the global carbon cycle. Using assimilation of ocean color satellite data into an ocean biogeochemical model, we estimate that global net ocean PP has experienced a small but significant decline −0.8 PgC y−1 (−2.1%) decade−1 (P