Ch. Pilskaln et al., Spatial and temporal dynamics in marine aggregate abundance, sinking rate and flux: Monterey Bay, central California, DEEP-SEA II, 45(8-9), 1998, pp. 1803-1837
Citations number
51
Categorie Soggetti
Aquatic Sciences","Earth Sciences
Journal title
DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY
Seasonal profiles of marine aggregate abundance and in situ sinking rate ex
periments were carried out using a uniquely instrumented ROV platform in th
e midwater column of Monterey Bay California between 1991 and 1994. Variati
ons of an order of magnitude in the midwater 100-500 m abundance of aggrega
tes within the 0.5 to > 5 mm size range were observed on an inter- and intr
a-annual basis at the study site. Maximum midwater aggregate abundances of
15-40 aggregates l(-1) were common during the 1991 spring/summer upwelling
season, with values of less than 5 aggregates l(-1) being more typical of t
he non-upwelling winter months and the 1992 El Nino period. Midwater aggreg
ate peaks represented the temporal signal of sinking aggregate material pro
duced in the overlying waters, with no correlation observed between the ver
tical distribution of aggregates and the density structure, or the relative
suspended particle abundence measured as c(p). Additionally, significant i
njection of aggregate material to the midwater profiles via lateral advecti
on was not evidenced by the combined aggregate, hydrographic, and physical
flow data sets obtained simultaneously at the study site. In situ aggregate
sinking rates were measured using an ROV-mounted settling chamber. Mean ra
tes ranged from 16.3 to 25.5 m day(-1) with a trend of increasing sinking r
ate with aggregate diameter observed. An analysis of aggregate shape showed
a decrease in spherical shape with increasing aggregate diameter and sinki
ng rate. Seasonal aggregate POC fluxes at 450 m for 1991-1992 were calculat
ed from the in situ aggregate property data sets to compare with coincident
, 450 m trap-measured POC fluxes. The calculated aggregate POC fluxes range
d from 26.3 to 481.2 mgC m(-2) d(-1) and were at least 1.5-2 times greater
than the trap POC fluxes, with the exception of the non-upwelling winter mo
nths where values are similar. Trapping efficiency and interannual variatio
ns in aggregate sinking rates are believed to explain the differences betwe
en the aggregate and trap-based POC fluxes. (C) 1998 Published by Elsevier
Science Ltd. AU right reserved.