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BIOGEOCHEMISTRY OF THE ANAXIMENES SEAMOUNT (E.MEDITERRANEAN): MOLECULAR EVIDENCE FOR A
“SEAMOUNT EFFECT” IN PARTICULATE ORGANIC MATTER QUALITY?
Kostas Kiriakoulakis1,2 and George Wolff2
1 Liverpool John Moores University, School of Natural Sciences and Psychology, [email protected]
2 University of Liverpool, School of Environmental Sciences,, [email protected]
Global estimates of seamounts
33452 seamounts (4.7%) and 138412 knolls (16.3%) globally (Yesson et al. 2011)
(Yesson et al. 2011)
seamounts
knolls
Observations and theories
• Less than 300 have been studied in some degree
• “Hotspots” of marine life and diversity
– Large pelagic (fish stocks and zooplankton) and benthic biomass (e.g. cold water corals etc.)
– ‘Island’ theory: Endemism – not much evidence
– ‘Oasis’ theory: productive in an otherwise nutrient depleted ocean – open question
Complex physics
Upwelling ⇒
High primary production
Closed circulation :Taylor columns
(e.g. White et al. 2007)
• Particle retention?
• Zooplankton migration blockage?
Effect on carbon cycling?
DOC
Mather 2009
Downwelling of DOC above topography
36°N
CD1712005
Is there a “Seamount effect” in the ocean?
• Enhanced local primary/secondary productivity, trapping of advected particles?
• Temporal variability?
• Primary production is seasonal
• Taylor columns are (thought to be) transient features
• Nutritional status of the ecosystems?
• Quality of organic matter
• Can be assessed by molecular studies (e.g. lipid biomarkers)
PUFAs: markers of POM quality
PUFAs: Poly-Unsaturated Fatty Acids
• Essential fatty acids
• Very labile (1/2 life ~ < 1 week) and energy rich
• Markers of (high) OM quality
Docosahexaenoic acid (DHA) - Dinoflagellates
Eicosapentaenoic acid (EPA) - Diatoms
Lipids of known biological origin
Quality of POM: link with zooplankton?
Martin and Christiansen 2009
Zooplankton biomass Spring 2003
day
nig
ht
Seineseamount
Seineseamount
0
10
20
30
40
50
60
% lipids
PUFAs
0
5
10
15
20
25
µg L-1
POC
top
South
North
Far
Data from Kiriakoulakis et al. 2009
Anaximenes Seamount• Within very oligotrophic, warm (even at depth) waters
• Part of Anaximander Mountains complex
• Elongated summit at ~700 m, eastern trough at ~1600 m
• Comparison with a reference site (Northern Rhodes Basin ~4300 m)
Map is modified from ten Veen et al. (2004).
In situ pump (SAPS)• Suspended particles (best sampled with SAPS)
Sampling scheme
50m euphotic layer
Close to bottom (10-20mab)
150m below euphotic layer
Summit (3)Control (1) Trough (2)
Northern Rhodes Basin
Anaximenes
Between Anaximenes and Anaxagoras
Particulate Organic C and N
10
100
1000
10000
0 5 10 15 20 25 30
Sam
plin
g D
epth
(m
)
µg L-1 water
POC
control summit 1 summit 2
summit 3 trough 1 trouph 2
10
100
1000
10000
0 1 2 3 4 5
Sam
plin
g D
epth
(m
)
µg L-1 water
PN
control summit 1 summit 2
summit 3 trough 1 trouph 2
• Variable POC and PN concentrations close to surface
• Lowest POC at reference site (one sample only)
• Exponential decrease of POC with depth but not for PN
• Unclear interpretation for PN: relation to atmospheric N input and P limitation in the region?
Particulate Lipids
• Lowest [lipids] at reference site
• Fatty acids (and PUFAs) almost disappear below euphotic layer
• Simultaneously heterotrophic signal increases at depth
• Lower quality suspended POM at depth
Modified OM markers (zooplankton + faecal pellets)
Particulate Lipids
• Statistically significant compositional differences between surface (50 m) and deeper waters
• Except surface sample at control site (Northern Rhodes Basin): similar composition to deeper waters = not good OM quality
Seamount effect?
Seamount effect? • Can’t say with only one sample (although 50 variables!) but intriguing
• Denda and Christiansen 2011 did not find ‘seamount effect’ in zooplankton (same cruise)
• They suggest that larger-scale structures of cyclones and anticyclones, dominate circulation in the area
Denda and Christiansen 2011
AMC: Asia Minor Current; MMJ: Mid-Mediterranean Jet
The jury is still out
Thank you for listening!
• Many thanks to:
• The Crew and Master of RV Meteor 71/1
• CENSEAM for funding this research
