The distribution of dissolved zinc in
the South Atlantic as part of the UK
GEOTRACES Programme
N. Wyatt1, A. Milne1, M. Woodward2 G. Henderson3, P. Worsfold1,
M. Lohan1
1. Plymouth University, UK
2. Plymouth Marine Laboratory, UK
3. University of Oxford, UK
UK GEOTRACES
Zinc
• Zinc is a required metal for bacteria and phytoplankton.
• Serves as a metal cofactor for important processes, most
notably for nucleic acid transcription and repair proteins, in the
enzyme alkaline phosphatase and for CO2 uptake via the
enzyme carbonic anhydrase.
• Vertical profile strongly correlated to the macronutrients
Si(OH)4, NO3- and PO43-, suggesting a role for zinc in ocean
biogeochemical cycles.
• Seawater dZn concentrations range from <10 pM in surface
waters to >8 nM in deep waters.
• Minor component (~70 ppm) of continental crust
• Highly contamination prone element
The South Atlantic at 40o S
40o S
Satellite derived global chlorophyll concentrations (Sigman and Hain, 2012)
Sampling and Analysis
Left: Cruise transect map
Above: R.R.S James Cook, Cape
Town S.A.
Sampling and Analysis
•
Samples collected to ~5200 m using TM clean Ti
CTD rosette
•
Surface (10 m) samples collected by towed FISH
•
Filtered through 0.2 µm cartridge filter
•
Total dissolved Zn determined by FIA-FL (Nowicki
et al., 1994; Gosnell and Landing, 2012)
•
Nutrient samples analysed by segmented flow
colorimetric auto-analysis (Woodward and Rees,
2001)
D357 Total dissolved zinc
1st transect
2nd transect
•
•
Dissolved zinc concentrations range 15 pM –
8.2 nM
Concentrations generally increase with depth
but slightly decrease between 1500 – 2500 m
JC068 Total dissolved zinc
•
•
Dissolved zinc concentrations range 15 pM –
8.2 nM
Concentrations generally increase with depth
but slightly decrease between 1500 – 2500 m
JC068+D357 Total dissolved zinc
•
•
•
JC068 with D357 1000 m intergrated.
Dissolved zinc concentrations range 15 pM –
8.2 nM.
Concentrations generally increase with depth
but slightly decrease between 1500 – 2500 m
Crossover station 3
Silicate
Zinc
0
2
nM
4
6
0
8
20
40
60
uM
80
100 120 140
0
0
1000
1000
JC068
2000
Depth m
JC068
D357
3000
4000
5000
Depth m
2000
3000
4000
5000
D357
dZn distribution controlled by water masses
UCDW
UCDW
NADW
AABW
NADW
AABW
AAIW
UCDW
NADW
AABW
AABW
JC068 Zn vs. Si
AABW
AABW
n = 348
•
Strong Zn/Si relationship
primarily due to uptake and
regeneration of Zn by
diatoms.
•
Surface ratio lower due to
biological uptake.
•
Deep water (> 3000 m) ratio
suggests a slight
underestimation of dZn by
up to 6 % in South Atlantic
bottom waters.
Location
Slope
R2
n
Global deepwater
>1000 m
0.052
0.988
211
0.054
0.992
43
0.059
0.941
10
0.040
0.859
130
0.038
0.828
11
0.061
0.981
348
North Pacific
Drake Passage
Southern Ocean
Polar Front 49°
59´ S
South Atlantic
Reference
Marchitto et al.
(2000)
Bruland (1980)
Martin et al.
(1990)
Croot et al.
(2011)
Löscher et al.
(1999)
This study
Low Zn D357 – Transect 1
• Zinc and silicate nutricline 500 – 700 m
• Nitrate and phosphate nutricline 100 – 400 m
• Low zinc concentrations likely linked with the Southern
Ocean nutrient return path
Low Zn JC068
• Zinc and silicate nutricline 500 – 700 m
• Nitrate and phosphate nutricline 100 – 400 m
• Low zinc concentrations likely linked with the Southern
Ocean nutrient return path
Southern Ocean supply of nutrients
UCDW
NADW
AABW
40o S
Nitrate data from one of 24 WOCE sections in the Atlantic
40o S
40o S
UCDW
UCDW
NADW
AABW
NADW
AABW
UK GEOTRACES
SAMW and Si* tracer
Sarmiento et al. (2004)
•
SAMW is main nutrient return path from deep waters of the
Southern Ocean to the thermocline of global ocean.
•
SAMW characterised by high nitrate but low silicate.
•
Si* = Si(OH)4 – NO3- used to trace movement of SAMW.
SAMW and Si* tracer
SAMW
Future work
•
Co analysis for D357 and JC068 – November 2012. I will look into
the potential limitation patterns of Zn and Co over the three
transects. I would hope to recruit the help of Heather and Tom and
potential look at their phytoplankton data to determine the groups
present along 40 S.
•
Argentine Basin core samples. The high concentrations of Zn at
depth may prove an interesting story and we can now potentially
look at the Zn within the core samples. Thanks Will.
•
Papers. Hopefully two, one based on the Zn/Co distribution across
the entire transect and one focusing on the Cape basin seasonal
changes in Zn/Co and their potential for limiting biological
production.
•
Particulates?
Summary
• Zinc is a required metal for bacteria and phytoplankton.
• Our aim was to measure dissolved zinc concentrations along 40o S
transect and to determine the process that control its distribution
and examine the role of zinc in controlling productivity.
• Dissolved zinc concentrations ranged 15 pM – 8.2 nM.
• The zinc concentrations along 40o S are primarily controlled by the
water masses that occupy the area.
• We found a significant (R2 0.98) correlation between dissolved zinc
and silicate for the entire transect and a