Journal of Oceanography, Vol. 62 (No. 6), pp. 873-885, 2006
Óscar A. Barocio-León1*, Roberto Millán-Núñez1, Eduardo Santamaría-del-Ángel1, Adriana González-Silvera1 and Charles C. Trees2
1Universidad Autónoma de Baja California, Facultad de Ciencias Marinas, Km. 103 Carretera Tijuana-Ensenada, Ensenada, Baja California, CP. 22800, México
2Center for Hydro-Optics and Remote Sensing, San Diego State University, 605 Alvarado Road, Suite 206, San Diego, CA 92120-5005, U.S.A.
(Received 2 December 2005; in revised form 28 April 2006; accepted 19 July 2006)
Abstract: We have estimated the spatial variability of phytoplankton specific absorption coefficients (a*ph) in the water column of the California Current System during November 2002, taking into account the variability in pigment composition and phytoplankton community structure and size. Oligotrophic conditions (surface Chl < 0.2 mg m-3) dominated offshore, while mesotrophic conditions (surface Chl 0.2 to 2.0 mg m-3) where found inshore. The specific absorption coefficient at 440 [a*ph(440)] ranged from 0.025-0.281 m2mg-1 while at 675 nm [a*ph(675)] it varied between 0.014 and 0.087 m2mg-1. The implementation of a size index based on HPLC data showed the community structure was dominated by picoplankton. This would reduce the package effect in the variability of a*ph(675). Normalized aph curves were classified in two groups according to their shape, separating all spectra with peaks between 440 and 550 nm as the second group. Most samples in the first group were from surface layers, while the second group were from the deep chlorophyll maximum or deeper. Accessory photoprotective pigments (APP) tended to decrease with depth and accessory photosynthetic pigments (APS) to increase, indicating the importance of photoprotective mechanisms in surface layers and adaptation to low light at depth. Samples with higher ratios of APP:APS (>0.4) were considered as phytoplankton adapted to high irradiances, and lower ratios (<0.26) as adapted to low irradiances. We found a good relationship between APP:APS and a*ph(440) for the deeper layer (DCM and below), but no clear evidence of the factors causing the variability of a*ph(440) in the upper layer.