Comparison of Phytoplankton Dynamics in the North Atlantic and the North Pacific

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North Pacific North Atlantic

Temporal standard deviationof chlorophyll (mg m-3)

Temporal standard deviationof chlorophyll (mg m-3)

Temporal standard deviationof carbon biomass (mg m-3)

Temporal standard deviationof carbon biomass (mg m-3)

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North Atlantic Box19ºW - 21ºW, 49.5ºN - 50.5ºN

North Pacific Box144ºW - 146ºW, 49.5ºN - 50.5ºN

Chlorophyll

PhytoplanktonCarbon fromParticulateBackscatter(Behrenfeld et al., 2005)

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North Atlantic Box19ºW - 21ºW, 49.5ºN - 50.5ºN

North Pacific Box144ºW - 146ºW, 49.5ºN - 50.5ºN

Chl:C Ratio

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Observed Chl:C ratios at OSPMeasurements at OSP (Varela & Harrison, 1999)

Mar-93 Feb-94 May-93 May-94 Sep-92 Sep-94

Chl mg m-2 14.6 12.4 23.2 14.2 35.1 19.7

PN mg m-2 43.5 60.6 67.2 69.2 111.5 77.5

PC mg m-2 696 969.6 1075.2 1107.2 1784 1240

Chl:C 0.021 0.013 0.022 0.013 0.020 0.016

Feb Mar Apr May Jun Jul Aug Sep

1992 0.020

1993 0.021 0.022

1994 0.013 0.013 0.016

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Full Time Series

Chlorophyll

PhytoplanktonCarbon fromParticulateBackscatter(Behrenfeld et al., 2005)

Atlantic: 20ºW-40ºWPacific: 160ºW-140ºW

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Full Time SeriesAtlantic: 20ºW-40ºWPacific: 160ºW-140ºW

Chl:C Ratio

Why are summer Chl:C ratios lower in the Pacific than the Atlantic?

More light in the Pacific? Stronger nutrient stress in the Pacific?

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�Geider Model:

max = b / (1 + b • a • I / (2 • Pcmax)) + a

b = 0.038 mg Chl / mg C, a = 0.002 mg Chl / mg C

a = 3.0E-5 gChl-1 gC W-1 m2 s-1, Pcmax = 3.0E-5 s-1

I = growth irradiance (W m-2)

Atlantic

Atlantic

Atlantic

Pacific Pacific

Pacific

Chlorophyll:Carbon RatioObserved Chl:C Growth Irradiance Ig

Calc. Chl:C = f(Ig)

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Chlorophyll:Carbon Ratio

observed

calculated

observed

calculated

Atlantic

Pacific

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Chlorophyll:Carbon Ratio

observed

calculated

observed

calculated

Atlantic

Pacific

Atlantic

Pacific

�Nutrient (and Temperature) Limitation Index:

f(N,T) = obs / max

obs = observed Chl:C

max = calc. max. Chl:C from Geider, assuming no nutrient limitation

No growth limitation

Strong growth limitation

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Chlorophyll:Carbon Ratio

observed

calculated

observed

calculated

Atlantic

Pacific

Atlantic

Pacific

No growth limitation

Strong growth limitation

Atlantic

Pacific

Fan et al., subm.

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Soluble Fe Flux (Fan et al., submitted)

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Opal Flux (Wong & Matear, 1999)

Ocean Station P, Sediment Trap Data

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Particulate Backscatter (Stramski et al., 2004)

“More recently, it was suggested that in typical non-bloom open ocean waters,

phytoplankton or all the microorganisms account for a relatively small fraction of

particulate backscattering, and that most of the backscattering may be due to non-living

particles, mainly from the submicron size range (Morel & Ahn, 1991; Stramski &

Kiefer, 1991). The potential role of small-sized organic detritus as a major source of

backscattering was emphasized but the significance of minerals was not excluded (see

also Stramski, Bricaud, & Morel, 2001). (…)

The optical impact of coccolithophorid phytoplankton (coccolithophores) can be,

however, very important (Balch, Kilpatrick, Holligan, Harbour, & Fernandez, 1996).

These phytoplankton species produce calcite scales called coccoliths that are

characterized by a high refractive index. It was estimated that even outside the

coccolithophore bloom, 5–30% of the total backscattering could be associated with

coccoliths (calcite plates detached from cells) and plated cells.”

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17

Coccoliths (Balch et al., 2005)

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19

Mesozooplankton (Goldblatt et al., 1999)

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Bacterial Biomass (Sherry et al., 1999)

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Full Time SeriesAveraged: 20ºW-40ºWAveraged: 160ºW-140ºW

MaximumChl:C Ratio

NutrientLimitationFactor