How does rising atmospheric CO2 affect marine organisms?

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Elk Island National Park, East-Central Alberta, Canada
Campbell, I.D. and Campbell, C. 2000. Late Holocene vegetation and fire history at the southern boreal forest margin in Alberta, Canada. Palaeogeography, Palaeoclimatology, Palaeoecology 164: 279-296.

The authors analyzed pollen and charcoal records obtained from sediment cores retrieved from three small ponds -- South Pond (AD 1655-1993), Birch Island Pond (AD 1499-1993) and Pen 5 Pond (400 BC-AD 1993) -- located in Canada's Elk Island National Park, which covers close to 200 km2 of the Beaver Hills region of east-central Alberta (~25 km east of Edmonton). In doing so, they discovered that "declining groundwater levels during the Medieval Warm Period allowed the replacement of substantial areas of shrub birch with the less fire-prone aspen, causing a decline in fire frequency and/or severity, as indicated by their Pen 5 Pond data; and they concluded that this scenario "is likely playing out again today," as all three of the sites they studied "show historic increases in Populus pollen and declines in charcoal." Furthermore, since their Pen 5 Pond data indicate that sediment charcoal concentrations have not yet dropped to the level characteristic of the MWP -- even with what they describe as the help of "active fire suppression in the park combined with what may be thought of as unintentional fire suppression due to agricultural activity around the park" -- it would appear that their study sites and their surroundings have not yet attained the level of warmth and dryness they experienced during the MWP, which they describe as having occurred over the period AD 800-1200.