Details

Autor(en) / Beteiligte

• Chen, C.-T. A
• Huang, T.-H
• Chen, Y.-C
• Bai, Y
• He, X
• Kang, Y

Titel

Air-sea exchanges of CO.sub.2 in the world's coastal seas

Ist Teil von

• Biogeosciences, 2013-10, Vol.10 (10), p.6509

Ort / Verlag

Copernicus GmbH

Erscheinungsjahr

2013

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• The air-sea exchanges of CO.sub.2 in the world's 165 estuaries and 87 continental shelves are evaluated. Generally and in all seasons, upper estuaries with salinities of less than two are strong sources of CO.sub.2 (39 ± 56 mol C m.sup.-2 yr.sup.-1, positive flux indicates that the water is losing CO.sub.2 to the atmosphere); mid-estuaries with salinities of between 2 and 25 are moderate sources (17.5 ± 34 mol C m.sup.-2 yr.sup.-1) and lower estuaries with salinities of more than 25 are weak sources (8.4 ± 14 mol C m.sup.-2 yr.sup.-1). With respect to latitude, estuaries between 23.5 and 50° N have the largest flux per unit area (63 ± 101 mmol C m.sup.-2 d.sup.-1 ); these are followed by lower-latitude estuaries (23.5-0° S: 44 ± 29 mmol C m.sup.-2 d.sup.-1 ; 0-23.5° N: 39 ± 55 mmol C m.sup.-2 d.sup.-1 ), and then regions north of 50° N (36 ± 91 mmol C m.sup.-2 d.sup.-1). Estuaries south of 50° S have the smallest flux per unit area (9.5 ± 12 mmol C m.sup.-2 d.sup.-1). Mixing with low-pCO.sub.2 shelf waters, water temperature, residence time and the complexity of the biogeochemistry are major factors that govern the pCO.sub.2 in estuaries, but wind speed, seldom discussed, is critical to controlling the air-water exchanges of CO.sub.2 . The total annual release of CO.sub.2 from the world's estuaries is now estimated to be 0.10 Pg C yr.sup.-1, which is much lower than published values mainly because of the contribution of a considerable amount of heretofore unpublished or new data from Asia and the Arctic. The Asian data, although indicating high pCO.sub.2, are low in sea-to-air fluxes because of low wind speeds. Previously determined flux values rely heavily on data from Europe and North America, where pCO.sub.2 is lower but wind speeds are much higher, such that the CO.sub.2 fluxes are higher than in Asia. Newly emerged CO.sub.2 flux data in the Arctic reveal that estuaries there mostly absorb rather than release CO.sub.2 . Most continental shelves, and especially those at high latitude, are undersaturated in terms of CO.sub.2 and absorb CO.sub.2 from the atmosphere in all seasons. Shelves between 0 and 23.5° S are on average a weak source and have a small flux per unit area of CO.sub.2 to the atmosphere. Water temperature, the spreading of river plumes, upwelling, and biological production seem to be the main factors in determining pCO.sub.2 in the shelves. Wind speed, again, is critical because at high latitudes, the winds tend to be strong. Since the surface water pCO.sub.2 values are low, the air-to-sea fluxes are high in regions above 50° N and below 50° S. At low latitudes, the winds tend to be weak, so the sea-to-air CO.sub.2 flux is small. Overall, the world's continental shelves absorb 0.4 Pg C yr.sup.-1 from the atmosphere.