Kw. Bruland et al., Iron and macronutrients in California coastal upwelling regimes: Implications for diatom blooms, LIMN OCEAN, 46(7), 2001, pp. 1661-1674
The supply of iron, relative to that of the macronutrients nitrate, phospha
te, and silicic acid, plays a critical role in allowing extensive diatom bl
ooms to develop in coastal upwelling regimes. The presence or absence of a
broad continental shelf influences the supply of iron, The iron input to ce
ntral California upwelling waters varies spatially and can be characterized
by two end-member regimes. One end member, which includes Monterey Bay and
extending north to Pt. Reyes, is an iron-replete regime where upwelling oc
curs over a relatively broad continental shelf that results in waters with
high concentrations of dissolved and particulate iron (>10 nM) entrained to
gether with high concentrations of nitrate and silicic acid. In these iron-
replete regions, extensive blooms of large diatoms deplete macronutrient co
ncentrations, which results in correspondingly high chlorophyll a concentra
tions. The other end member, located to the south of Monterey Bay off the B
ig Sur coast, is an iron-deplete regime where upwelling is focused offshore
of a narrow continental shelf. Upwelled waters in the Big Sur region are c
haracterized by low dissolved and particulate iron concentrations (<1 nM),
together with high concentrations of nitrate and silicic acid. Extremely lo
w iron concentrations, unused nitrate and silicic acid, and a low abundance
of large diatoms characterize surface waters in these iron-deplete regions
, and thus represent coastal upwelling, high-nutrient, low-chlorophyll syst
ems limited by the micronutrient iron.