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AGU Ocean Sciences Meeting (Feb. 2002) COAST abstracts:


Linking Phytoplankton Fluorescence Patterns in the Nearshore and
Inner Shelf off Oregon

Ashe, A. L., M. R. Abbott, P. M. Kosro, B. A. Grantham and
R. M. Letelier

High frequency temperature, salinity, and chlorophyll fluorescence
records collected nearshore at the 15 m isobath off the Oregon Coast
at Fogarty Creek (FC; 44.84N, 124.06W), Whales Cove (WC; 44.79N,
124.16W), Yachats Beach (YB; 44.32N, 124.12W), and Strawberry
Hill (SH; 44.25N, 124.13W) during summer 2000 were analyzed and
compared to similar data recorded in the inner shelf at the 81 m
isobath off Newport (NH; 44.64N, 124.31W). Moored instruments in the
nearshore sites consisted of fluorometers and Seacats placed at 7 m
depth. The inner shelf mooring had similar instruments deployed at
5 m depth. Preliminary cross-correlation analyses indicate that
while the fluorescence signal in the southern nearshore sites
(YB and SH) displays a significant positive correlation with the
inner shelf signal with lag time of 0 days, the northern stations
(FC and WC) display only a weak but statistically significant
negative correlation with NH with a 4 day lag. Further analyses
of chlorophyll fluorescence in the temperature-salinity domain
indicate that fluorescence increases with increasing temperature and
a slight decrease in salinity. This pattern suggests that chlorophyll
concentration in the nearshore sites increases during relaxation
periods following upwelling events, probably as a result of the
advection of surface waters in which phytoplankton populations
have been growing. However, the northern nearshore sites display
a strong decrease in salinity during some relaxation events. These
water masses with high temperature and low salinity have relatively
low values in chlorophyll fluorescence. We suggest that this fresh
water intrusion in the northern nearshore stations holds back the
increase in chlorophyll concentration during relaxation events and
represents a key difference between these stations and inner shelf
and southern nearshore sites. This hypothesis is being tested with
an extended dataset collected between March and October 2001.

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