Labrador Sea convection blows life to the Northeastern Atlantic

Keywords: Ocean-shelf exchange, sub-decadal variability,

Predictability, Calanus finmarchicus

Hjálmar Hátún, Katja Lohmann, Selma Pacariz, Manfred Bersch Assthor Gislasson, Daniela Matei, Jón Ólafsson, Chris Reid and Johann Jungclaus

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http://www.frs.fo/default.asphttp://www.mpimet.mpg.de/

The energetic and productive North Atlantic Ocean

High (algae) concentrations

Ocean Color (chlorophyll-a)

The energetic and productive North Atlantic Ocean

m

Winter mixed layer depths (MLD)

Seasonal amplitude

Outline

1. The subpolar gyre - a main food source 2. Remote forcing from the Labrador Sea

to the Irminger Sea 3. Mixed Layer Depth (MLD) - a critical driver 4. The sub-arctic front 5. Predictability

Subtropical Gyre

Subpolar Gyre

Labrador Sea convection

The subpolar gyre - a main food source

(Hatun et al., Science 2005)

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Salinity in the Irminger Current (obs.)

Salinity at Rockall (obs.)

Gyre index Weak.

Strong

Mid-1990s Regime shift

(Hátún et al., 2009)

Salinity ‘dips’

The Subpolar Gyre - salinity ’dips’

or Great Salinity Anomalies

On-shelf biological production

MPIOM (Max Planck Institute Ocean Model)

(Matei et al., 2012)

Gyre index (high-passed)

Zooplankton

The Subpolar Gyre and on-shelf biological production

Strong gyre high production

PV

From: (Pickart, 2003)/(Talley & McCartney, 1982)

Convection

Degree of stratification

~ 1 yr

Nitrate

Silicate

(Concentrations in June, 50m)

The Subpolar Gyre: A large nutrient source

CPR

We’ll discuss nutrients next time

Green- land

Towing lines since the 1940s The subpolar gyre is a zooplankton epicenter

(Hátún, et al., 2009)

Average abundance of Calanus finmarchicus

The Subpolar Gyre: A large zooplankton source - Continuous Plankton Recorder (CPR)

South Iceland shelf

Mainly C. finmarchicus

Hypothesis: A north-eastward extended subpolar gyre limb in the Irminger Sea improves the biological productivity southwest of Iceland – both oceanic and potentially on the shelf.

2. Remote forcing advection from the Labrador Sea to the Irminger Sea

Is the zooplankton simply related to the North Atlantic Oscillation (NAO)?

NÃO

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Longitude

Latit

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Jan-April

Corr. coeff

Remote atmospheric forcing

MLD (in North IrB) vs. Heat loss

Atmospheric forcing: heat loss (W/m2) Not local

Greenland

Particle tracking experiment

Seeding Region (March)

Target region

Greenland

MPIOM

# pa

rtic

les

~ 1 year

3. Mixed Layer Depth (MLD) a critical driver

Mixed Layer Depth

Greenland

MLD

MPIOM

Simulated March Mixed Layer Depths (MLD) N. Irminger Sea (35-30°W, 61-63°N)

MLD and oceanic Calanus finmarchicus C. finmarchicus (adults)

Green- land

CPR

MLD

Oceanic and on-shelf zooplankton C. finmarchicus (adults)

Simulated March MLDs and zooplankton on the south Iceland shelf

Convection accentuates the ‘high-or-low’ variability

4. The biologically productive sub-arctic front

Finwhales (Víkingsson et al., 2009)

Mackerel in 2013 (PGNAPES)

Bluefin tuna (Mackenzie, Payne et al., 2014)

Redfish (Pedchenko, 2005)

EOF-upper ocean temperature (Hátún et al., 2005)

The biologically productive sub-arctic front

Front Index (MPIOM)

Shelf zooplankton

Frontal shift towards Iceland

Increased zooplankton abundance when the sub-arctic front is shifted towards Iceland

Heat loss

Labrador Sea

Heat loss

Iceland shelf

Increase early Prim. Prod.

On-shelf Prim. Prod.

‘Phyto-convection’ (Backhaus et al., 1999) and/or ‘Dilution-Recoupling’ (Behrenfeld, 2010)

Highly nutrient rich

Mixed Layer Depth (MLD) - a critical parameter

Let’s re-cap

Green- land

Lab Sea

Heat loss

Lab Sea

Heat loss

Iceland shelf

Highly nutrient rich

Jan

Apr

Jul

Oct

Dec

Seeded 1/4 year 2000, depth 6

MPIOM: Particle tracking

~ 1-4 months

1-4 months

Jan

Apr

Jul

Oct

Dec

y p

MPIOM: Particle tracking

5. Predictability

10.5 months lead Start in June

Ranked probability skill score

SST Predictability Intra-seasonal to inter-annual

Seasonal forecasting system. US National Multi-Model Ensemble (NMME)

Ranked probability skill score

US National Multi-Model Ensemble (NMME) seasonal forecasting system.

SST Predictability Intra-seasonal to inter-annual

10.5 months lead Start in March Amongst the highest predictability

potential in the World

Stronger convection again in 2012 and 2014: We predict(ed) increased production

Messages

• A north-eastward extended subpolar gyre limb in the Irminger Sea improves the biological productivity southwest of Iceland – both oceanic and potentially on the shelf

• Mechanistic understanding potential for

prediction (0.5 to 1.5 years ahead)

The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299 NACLIM www.naclim.eu

http://www.naclim.eu/

Labrador Sea convection� blows life to the Northeastern AtlanticThe energetic and productive� North Atlantic OceanThe energetic and productive� North Atlantic OceanOutlineSlide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 102. Remote forcing advection from the Labrador Sea to the Irminger Sea�Slide Number 13Particle tracking �experiment3. Mixed Layer Depth (MLD) �a critical driver�Mixed Layer DepthSimulated March Mixed Layer Depths (MLD)�N. Irminger Sea (35-30°W, 61-63°N)MLD and oceanic Calanus finmarchicusOceanic and on-shelf zooplanktonSimulated March MLDs and� zooplankton on the south Iceland shelf4. The biologically productive�sub-arctic frontSlide Number 22Slide Number 23Slide Number 245. Predictability SST Predictability �Intra-seasonal to inter-annualSST Predictability �Intra-seasonal to inter-annualMessagesSlide Number 29