No abstract

A time series of chlorophyll a and in situ primary production sampled over a period of 33 days during summer in Ubatuba region, southeastem Brazil, was subjected to multivariate and harmonic analysis. Principal Component Analysis has revealed four factors interpreted as (i) South Atlantic Central Water forcing; (ii) Transient ftontal systems and rain fali forcings; (iii) Wind forcing normal to the coast; (iv) Wind forcing parallel to the coast, as main factors in the variability of the phytoplankton biomass and primary productivity. Splitting of the time series according to four main events which had profound effects on the physicochemical characteristics of the region showed the following variations in the primary productivity integrated over the photic layer (g C m-2 day-1): mixing→stratification period, 0.40 ± 0.11; heavy rainfall, 1.24± 0.28; stratification after rainfall, 0.74± 0.10; stratification→mixing period, 0.90± 0.27; stratification after deep mixing, 0.63 ± 0.28. Harmonic analysis revealed two indistinguishable significant peaks of the phytoplankton biomass - one at a period of 8.25 days and one at a period of 6.6 days, contributing, respectively, about 17 and 32% ofthe total variance. Atmospheric forcing showed a characteristic period,of 200-264 hours while phytoplankton biomass response ranged over the 144-192 hours time scales and primary productivity was best related to the environment 360 hours before. Relative to total nitrogen' and ' biomass primary productivity oscillations were lagged about 96-144 hours. The interruption of steady-state conditions by transient atmospheric ev~nts and wind field intensification are the determining factors driving phytoplankton changes in this coastal environment.
Uma série temporal de clorofila a e produção primária obtida em um período de 33 dias durante o verão na região de Ubatuba, sudeste do Brasil, foi submetida à análise multivariada e harmônica. A Análise de Componentes Principais revelou quatro fatores interpretados como (i) Água Central do Atlântico Sul; (ii) Sistemas ftontais transientes e chuvas; (iii) Ventos normais à costa; (iv) Ventos paralelos à costa. Estes fatores atuam como forçantes ambientais na determinação da variabilidade observada na biomassa fitoplanctônica e produtividade primária. A divisão da séríe temporal de acordo com quatro eventos modificadores das características fisicoquímicas da região mostrou a seguinte variabilidade na produção primária integrada (g C m,2 dia,l) na camada eufótica: coluna de água homogênea em processo de estratificação térmica- 0,4O±0, 11; coluna de água estratificada e chuvas intensas- 1,24±0,28; coluna de água misturada em fase de estratificação térmica após intensas chuvas- 0,74:f:0,10; coluna de água estratificada em fase de processo de mistura- 0,90±0,27; coluna de água homogênea em fase de estratifição térmica após intensa mistura- 0,63±0,28. A Análise Harmônica revelou dois picos de biomassa significativos- um com período de 8,25 dias e outro com período de 6,6 dias, contribuindo, res...

No abstract

A time series of chlorophyll a and in situ primary production sampled over a period of 33 days during summer in Ubatuba region, southeastem Brazil, was subjected to multivariate and harmonic analysis. Principal Component Analysis has revealed four factors interpreted as (i) South Atlantic Central Water forcing; (ii) Transient ftontal systems and rain fali forcings; (iii) Wind forcing normal to the coast; (iv) Wind forcing parallel to the coast, as main factors in the variability of the phytoplankton biomass and primary productivity. Splitting of the time series according to four main events which had profound effects on the physicochemical characteristics of the region showed the following variations in the primary productivity integrated over the photic layer (g C m-2 day-1): mixing→stratification period, 0.40 ± 0.11; heavy rainfall, 1.24± 0.28; stratification after rainfall, 0.74± 0.10; stratification→mixing period, 0.90± 0.27; stratification after deep mixing, 0.63 ± 0.28. Harmonic analysis revealed two indistinguishable significant peaks of the phytoplankton biomass - one at a period of 8.25 days and one at a period of 6.6 days, contributing, respectively, about 17 and 32% ofthe total variance. Atmospheric forcing showed a characteristic period,of 200-264 hours while phytoplankton biomass response ranged over the 144-192 hours time scales and primary productivity was best related to the environment 360 hours before. Relative to total nitrogen' and ' biomass primary productivity oscillations were lagged about 96-144 hours. The interruption of steady-state conditions by transient atmospheric ev~nts and wind field intensification are the determining factors driving phytoplankton changes in this coastal environment.