Primary production and community structure response to deep seawater enrichment Karin Björkman, PhD OTEC/SWAC meeting 16 September 2011

Nutrient enrichment experiments DSWCONTROL: MLSW (30 m) TREATMENT: MLSW + DSW (5% v/v) ~ 2 µmol L -1 N+N Depth (m) µmol SRP kg -1 Mahaffey et al. in review

3 Nutrient enrichment experiments Incubated on deck Sampled approx daily for 4-5 days Samples: Nutrients (N, P, Si) Pigments Rate measurements: Primary production ( 14 C) Mahaffey et al. in review CONTROL: MLSW (30 m) TREATMENT: MLSW + DSW (5% v/v) ~ 2 µmol L -1 N+N

Chlorophyll a – size fractionated distribution CONTROL Month Chl a (µg l -1 )

Chlorophyll a – size fractionated distribution CONTROL Month Chl a (µg l -1 ) Treatment 5% DSW Month Scale !

Primary production – size fractionated distribution CONTROL Month PP (µg C l -1 d -1 )

Primary production – size fractionated distribution CONTROL Month PP (µg C l -1 d -1 ) Treatment 5% DSW Month Scale !

Community structure- Diagnostic pigments Month CONTROL ng L -1

Community structure- Diagnostic pigments Month CONTROL Treatment 5% DSW Scale! ng L -1

10 General Results Always increases in phytoplankton biomass (chlorophyll) Always increases of primary production Population structure changed – Larger cells – Diatom biomarkers up Variable – – Magnitude in response – Dominant phytoplankton group