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| The distributions of biogenic and lithogenic silica concentrations and net silica production rates in the upper 120 m of the Eastern Equatorial Pacific (EEP) were examined in December 2004, on two transects situated at 110 degrees W (4 degrees N to 3 degrees S) and along the equator (110 degrees W to 140 degrees W). Lithogenic silica (ISiO(2)) was generally < 10 nmol Si 1(-1) with maximum concentrations reaching 25 nmol l(-1) in surface waters. These low concentrations confirm low atmospheric inputs of particulate Si, consistent with reported low inputs of wind-borne material in the EEP. In spite of active upwelling of silicic acid-rich waters the biogenic silica (bSiO(2)) concentrations were generally low, falling between 100 and 180 nmol Si 1(-1) in the upper 50m and decreasing to less than 50 nmol Si 1(-1) below similar to 90 m. Estimates of net bSiO(2) production rates revealed that the rate of production exceeded that of dissolution in the upper euphotic layer (0-40 m) along 110 degrees W with net production extending somewhat deeper (60-100 m) to the west along the equator. Net production rates in the surface layer were low, ranging between 5 and 40 nmol Si 1(-1) d(-1), consistent with previous observations that diatoms are small contributors to autotrophic biomass in the EEP. Net silica dissolution predominated in the lower euphotic layer (40-120 m), indicating active Si recycling which diminished the strength of the silica pump in this region. (C) 2010 Elsevier Ltd. All rights reserved. | |
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