School of Biological Sciences, Flinders University, PO Box 2100, Adelaide, South Australia 5001, Australia.
Proc Biol Sci. 2010 Nov 22;277(1699):3527-31. doi: 10.1098/rspb.2010.0863. Epub 2010 Jun 16.
The iron-limited Southern Ocean plays an important role in regulating atmospheric CO(2) levels. Marine mammal respiration has been proposed to decrease the efficiency of the Southern Ocean biological pump by returning photosynthetically fixed carbon to the atmosphere. Here, we show that by consuming prey at depth and defecating iron-rich liquid faeces into the photic zone, sperm whales (Physeter macrocephalus) instead stimulate new primary production and carbon export to the deep ocean. We estimate that Southern Ocean sperm whales defecate 50 tonnes of iron into the photic zone each year. Molar ratios of C(export):Fe(added) determined during natural ocean fertilization events are used to estimate the amount of carbon exported to the deep ocean in response to the iron defecated by sperm whales. We find that Southern Ocean sperm whales stimulate the export of 4 × 10(5) tonnes of carbon per year to the deep ocean and respire only 2 × 10(5) tonnes of carbon per year. By enhancing new primary production, the populations of 12 000 sperm whales in the Southern Ocean act as a carbon sink, removing 2 × 10(5) tonnes more carbon from the atmosphere than they add during respiration. The ability of the Southern Ocean to act as a carbon sink may have been diminished by large-scale removal of sperm whales during industrial whaling.
缺铁的南大洋在调节大气 CO2 水平方面发挥着重要作用。有人提出，海洋哺乳动物的呼吸作用会降低南大洋生物泵的效率，因为它们将光合作用固定的碳返还到大气中。在这里，我们表明，通过在深水区捕食猎物并将富含铁的液体粪便排到透光层，抹香鲸（Physeter macrocephalus）反而会刺激新的初级生产力和碳向深海的输出。我们估计，南大洋的抹香鲸每年将 50 吨铁排入透光层。在自然海洋施肥事件中确定的 C（输出）：Fe（添加）摩尔比用于估计由于抹香鲸排泄的铁而向深海输出的碳量。我们发现，南大洋的抹香鲸每年刺激 4×105 吨碳向深海输出，而每年仅呼吸 2×105 吨碳。通过增强新的初级生产力，南大洋的 12000 头抹香鲸种群成为一个碳汇，从大气中去除的碳量比它们在呼吸过程中添加的碳量多 2×105 吨。在工业捕鲸过程中大量捕杀抹香鲸，可能削弱了南大洋作为碳汇的能力。
