Remineralisation rates of sinking particles – K2

MP Gall, PW Boyd (NIWA)&

J Valdes (WHOI)

On VERTIGO we adopted 3 approaches to examining particleRemineralisation / Respiration

i) Shipboard MicrowinklerIncubations and ETS

ii) In situ respirationchambers

ii) In situ remineralisationof settling particles

Successful

A failureData on ETS and bacterial ecto-enzymes before endof 2006 (HOT data indicate bact assim. effic. of 10% or less

Methodology (i)

A DO sensor was deployed within the ‘inner sanctum’ of the sediment trap

Our cylinder was deployed at 150 m depth along with other CLAP and ball trapcylinders

A rotating ball design was employed to prevent swimmers enteringthe inner sanctum

Fill trap withwater from 200 mNO PRESERVATIVES

T=0

10 min

STOP

T=36 h T=72 h

DISSOLVED OXYGEN AND TEMPERATUREWAS MEASURED EVERY 10 MINUTES

Particles collected on upper surface of the ball once it stopped turning

The experiments

Three 72 h deployments 3 additional experimentsi) After deployment 3 the trap was placed in a tempControlled lab at atmospheric pressure and the Remineralisation signature was followed for a further 36 h

ii) The video nasty – acclimated Neocalanus spp.Were added to the water overlying the ball valve (whichWas coated with settled particles). Their behaviour was Filmed – both with the ball in a stationary and in rotatingState.

iii) A serial addition experiment was conducted with Neocalanus spp. – using microwinkler flasks to estimateTheir respiration rates

Turley (1993) DSR I “linear decrease in rates ofLeucine and thymidine incorporation with increasingPressure” at 200 atm rates were 1/3 to ½ of those at 1 atm

K2 234 Th flux

In deployment 1the 234 Th flux for the36 h collection period was around 600 dpmm-2 d-1

Data courtesy of KEN BUESSELER

Deploy 1

Year day 2005

212.0 212.5 213.0 213.5 214.0

O2

(um

ol L

-1)

0

2

4

6

8

Export flux (as O2) = 74.29 umol L-1 This equals 6.2/74.3 is 8% over 36 h

6.1 umol L-1

over 36 h

OXYGEN CONSUMPTION DUE TO PARTICLE REMINERALISATION

HOWEVER……

We recovered 9 copepodsNeocalanus cristatus from the inner sanctum at the end of the deployment

We set up a video of these animals at ambient temperature on the upper side of a ‘particle laden’ ball.It was clearly evident that they could ride the ball and access the innner sanctum

Deploy 2

Year day 2005

223.2 223.6 224.0 224.4 224.8

O2

(um

ol L

-1)

0

2

4

6

8

A FURTHER TRAP DEPLOYMENTS YIELDED COMPARABLEOXYGEN CONSUMPTION RATES – despite a marked decrease inSurface PP, EP, but not in b

WHAT DO THE DATA TELL US?

Export flux (expressed as O2) = 74.29 umol L-1 over 36 h At 150 m

So remineralisation equals 6.2/74.3 i.e. 8% over 36 h

However, the particles that remineralised are a complex mixture of fast and slowsinkers (<10 m to 400 m d-1)

150 m

Mixed layer 40 m

Fast sinkersCould be 600 m deeperIf it was not intercepted and remineralized in ourtrap