Primary Productivity

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Primary production in Arctic lakes, Lost Pack Lake, Nunavut

Chlorophyll a (mg/g, difference from the mean value)
Graph: primary production in Lost Pack Lake, Nunavut. Click for graphic description (new window).
Long Description for Primary production in Arctic lakes, Lost Pack Lake, Nunavut

This line graph displays the levels of chlorophyll a contained in the sediment of Lost Pack Lake, Nunavut. The change in chlorophyll a is plotted as the difference from the mean value, in milligrams of chlorophyll a per gram of sediment. From over 5,000 years ago to the late 19th century chlorophyll a levels remained stable, fluctuating slightly around and below the mean value (0.00 milligrams per gram). At the end of the 19th century levels of chlorophyll a began to increase very steeply, reaching approximately 0.06 milligrams per gram above the mean value by the early 2000s. An inset map shows the location of Lost Pack Lake, Nunavut, on Baffin Island.

Note: chlorophyll a is the main pigment found in plants and algae and is a measure of primary production. Values are inferred through spectral analysis of lake sediment cores.
Source: adapted from Michelutti et al., 200510

The figure shows chlorophyll a reconstructions from Lost Pack Lake, one of six Baffin Island lakes examined for long-term trends. All lakes show dramatic increases of inferred primary production within the most recently deposited sediment, following prolonged periods of comparatively low values.10 Dating of the sediment cores indicates that these rapid increases started in the late 19th century and continue to the present. The increases are a departure, in most lakes, from relatively stable levels of primary production that persisted for millennia. A widespread increase in freshwater production over much of northern Canada is also inferred from major shifts in species composition of algae in ponds and small lakes in many areas (also detected from studies of sediment cores).11, 12 The best explanation for this change in algae is climatic warming leading to longer ice-free growing seasons and associated changes in lake ecosystems.13, 14 The changes are most pronounced in the High Arctic, but similar shifts in algal species are found in many locations in the Northern Hemisphere – with changes being more recent in temperate latitudes.15

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Marine primary production

Total chlorophyll (mg/m3) in the North Pacific, 1908 to 2008
Graph: marine primary production in the North Pacific. Click for graphic description (new window).
Long Description for Marine primary production

This graph shows the change in marine primary production, measured as total chlorophyll, in milligrams per square metre of ocean, in the North Pacific ocean region, from 1908 to 2008. The average annual primary production values, plotted as points, are distributed widely. These values are overlain with a trend line showing an overall significant decline. Total chlorophyll declined approximately from 0.8 to 0.3 milligrams per square metre from 1908 to 2008. In the periods from 1908 to 1930 and from 2005 to 2008 the trend line is marked as being based on limited data and hence having lower confidence.

Note: trend (line) and average annual values (points) were estimated through statistical modeling. Dashed line represent parts of the trend based on limited data and hence with lower confidence.
Source: adapted from Boyce et al., 201016

Satellite measurements of ocean colour have shown variable decade-scale trends in marine primary production, including a short-term increase in primary production in the Arctic Ocean from 1998 to 2008.17, 18 A recent study16 extended the record by also using longer-term measurements of water transparency and chlorophyll concentrations. This study concluded that, over the past 110 years, primary production has declined in most of the world’s ocean regions.16 High-latitude regions, including the North Pacific, showed the greatest long-term declines. The global decline in the amount of phytoplankton is estimated at 1% per year, with a total decline of 40% since 1950. Shorterterm trends were related to climate oscillations, while the long-term declines were most strongly related to increasing sea-surface temperatures – which leads to less mixing of ocean waters, reducing the nutrient supply for phytoplankton. The exceptions are the Arctic and Antarctic oceans, where the causes of the observed long-term decreases in primary production are less clear, but may be related to increased wind intensity.16

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