Production and fate of organic carbon and
nitrogen in waters northwest of Svalbard
Lena Seuthe1
Maria Lund Paulsen2
Marit Reigstad1
Aud Larsen2
Mattias R. Cape3
Maria Vernet4
1
2
3
4
This talk investigates: 1) how total primary production is
divided between the dissolved and particulate phase
POM
(C, N)
total PP =
dissolved PP + particulate PP
DOM
(C, N)
PP: Primary Production
POM: Particulate Organic Carbon
DOM: Dissolved Organic Carbon
This talk investigates 2) the seasonal change in C and N
stoichiometry of dissolved organic matter
POM
(C, N)
total PP =
dissolved PP + particulate PP
DOM
(C, N)
Bacterial uptake
PP: Primary Production
POM: Particulate Organic Carbon
DOM: Dissolved Organic Carbon
The study embraced two different sampling strategies:
1. Measuring production
rates during spring- and
post-bloom conditions
(stations P1-P7)
Primary Production
Particulate
Dissolved
Bacterial Production
Bacterial C-demand
2. Measuring in-situ
concentration from
January to November
(colored dots)
Particulate (>0.7µm)
Carbon (POC)
Nitogen (PON)
Dissolved (<0.7µm)
Carbon (DOC)
Nitrogen (DON)
PP was NO3-based during the spring bloom in May, and
NH4-based under post-bloom conditions in August
Chlorophyll a (µg L-1)
6
Spring bloom
5
4
3
2
Post- bloom
1
0
Januar
March
NO3
[Reigstad et al. in prep.]
May
August
November
NH4
Particulate organic matter concentrations peaked with
spring bloom and remained relatively high until early winter
POC
50
PON
40
200
30
20
100
0
10
January
March
May
August
November
0
PON (µg C L-1)
POC (µg C L-1)
300
DOC concentrations followed the seasonal pattern of POM
with peak concentrations during the spring bloom
DOC (µg C L-1)
800
DOC
600
400
200
0
January
March
May
August
November
Dissolved primary production contributed a large fraction
to total NO3-based primary production in spring
19 %
Post-bloom
32 %
Spring bloom
0
5
10
Depth (m)
15
20
25
30
35
40
45
n = 3 stations
0
50
100
Percent Extracellular Release (%)
n = 3 stations
0
50
100
Percent Extracellular Release (%)
Percent extracellular release = 100 * dissolved PP/total PP
The high rates of dissolved primary production most likely
caused the accumulation of DOC seen in spring
DOC (µg C L-1)
800
DOC
600
400
200
0
January
March
May
August
November
In-situ concentrations are the result of the balance
between the rate of production and consumption
DOC (µg C L-1)
800
DOC
600
400
200
0
January
dissolvedMarch
PP
May
DOM
(C, N)
August
November
Bacterial
consumption
?
Bacteria did not consume all the DOC produced in the
surface waters during the spring bloom
Spring bloom
0
Post-bloom
5
10
Depth (m)
15
20
25
30
35
40
45
n = 3 stations
n = 3 stations
1
100
10000
Bacterial carbon demand (%)
1
100
10000
Bacterial carbon demand (%)
Percent bacterial carbon demand = 100 * BCD/dissolved PP
The DOM accumulating in May was highly enriched in
carbon as often seen during phytoplankton blooms
DOC (µg C L-1)
800
600
400
200
0
DOC : DON
DOC
80
January
March
May
August
November
January
March
May
August
November
60
40
20
0
The mechanism of DOM production can be estimated by
the correlation of dissolved and particulate PP
Phytoplankton physiology
(diffusion, excretion)
[Baines and Pace 1991, Teira et al. 2003]
Trophic interactions
(grazing, lysis)
Different mechanisms of DOM production predominated
under spring- and post-bloom conditions
Spring bloom
Phytoplankton physiology
Dissolved Primary Production
(µg C L-1 d-1)
1000
Post-bloom
Trophic interactions
100
10
1
0,1
0,01
0,001
0,001
0,1
10
1000
Particulate Primary Production
(µg C L-1 d-1)
0,001
0,1
10
1000
Particulate Primary Production
(µg C L-1 d-1)
Peak DON concentrations in summer most likely the result
of increased DON production due to trophic interactions
DOC
150
DON
600
100
400
50
200
0
January
March
May
August
November
0
DON (µg C L-1)
DOC (µg C L-1)
800
DON concentrations dropped below winter concentrations
during spring – DON consumption by prokaryotes?
DOC
150
DON
600
100
400
50
200
0
January
March
May
August
November
0
DON (µg C L-1)
DOC (µg C L-1)
800
In summary, a large fraction of the NO3-based primary
production went into the dissolved phase in spring
DOC and DON accumulated asynchronously most likely due
to different production mechanisms
Early spring
winter DON
?
spring DON
Spring bloom
Post-bloom