Flashcards in Chemical Oceanography Deck (85):
1
P:N:C:O2
1:16:106:153
2
Nitrate
NO3 ^-
3
Phosphate
PO4 ^ 3-
4
ocean circulation
~1000yrs
5
least reactive major ion
Cl-
6
main barrier to ocean mixing
density difference (hence 2 box model)
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Ammonia
NH4+
8
Average mix layer
~70m
9
Anoxic waters have
higher burial (recall fish farming)
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Largest inputs and outputs
mixing and particle flux >> river input, burial
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(–) AOU
supersaturation
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Nitrite
NO2-
13
In a CaCO3 dominant system
surface has decreased Alk,
decreased [CO3 2-]
pH lower
fCO2 higher
atm CO2 higher
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NH4 comes from
respiration product
15
what happens to NH4 in surface
converted to NO2, NO3 (only in aerobic/oxic zone)
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local surface max in NH4
lag in the conversion from
respiration –– NH4+ –– NO2- –– NO3-
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Nitrification
NH4 + O2 –– NO2- –– NO3-
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Nitrogen Fixation
N2 ––– NH4+
N2 gas from the atmosphere
requires high Fe
19
expected NH4+ profile
low [ ] in surface water - possible small max from respiration
major increase is after o-a boundary
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expected NO3- profile
[low/0] right at surface (productivity)
increases throughout surface layer, fairly high max ~1000m (respiration)
anoxic - decreases back to 0 toward o-a boundary
open ocean - remains ~ stable with depth
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Expected NO2- profile
similar to NO3- but much smaller peak
small peak in oxygen layer from nitrification processes
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high N2
denitrification
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Conservative ions
only affected by evaporation and precipitation
no big fluctuations with depth
[ion] : seawater S remains ~constant
Mg, Na, Ca, Cl-
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Gases
affected by T, S, P, f, reactivity
increase with depth (lower T), except O2
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Bioactive elements
affected by primary production, respiration, remineralization
P, N, Fe, O2
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Trace metals
Very low concentrations
Mg, Fe, Co, Ni, Cu, Zn, Cd
27
Oxygen profile without biology
controlled by T like other gases
increase with depth
28
Oxygen along thermohaline
depleted
successive losses from respiration
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AOU
[O2]equil – [O2]meas
Apparent Oxygen Utilization
amount respired
oxygen deficit due to respiration
~ opposite to oxygen curve
30
typical O2 profile
minimum above 1000m (respiration)
increase after 1000m (horizontal advection from O2 rich high latitude (cold) waters)
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Ventilation impact on O2, AOU
larger ventilation (age, older)
lower O2
higher AOU
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OUR
Oxygen Utilization Rate
mean respiration rate in the water parcel since it left the surface
AOU / Age
high at surface, decrease with depth
33
AOU profile
low at surface
max at O2 min (~500-1000m)
decrease with depth
34
Oxygen minimum occurs
medium age
medium respiration
35
Carbonate weathering reactions
CaCO3 + CO2 + H2O –– Ca2+ + 2HCO3-
2HCO3- + Ca2+ –– CaCO3 + CO2 + H2O
36
low [surface nutrient] affects on fCO2
low [surface nut.] = low fCO2
high P flux –– low [nut.] –– low C (by RKR) –– low DIC –– low CO2 –– low fCO2
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high [surface nutrients], fCO2
high DIC = high fCO2
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Phosphate characteristics
enriched along thermohaline
bioactive, typical bioactive curve
high in S ocean (HNLC)
controlled by photosynthesis and respiration
39
DIP_preformed
Preformed = Total – Respired
(DIP_T) – (r_P:O2 x O2_respired)
(DIP_T) – (r_P:O2 x AOU)
Preformed phosphate
portion of P advected to deep irrespective of respiration
40
DIP respired
= AOU x (P/O2)
i.e. r_P:O2 x AOU
41
Phosphate, Nitrate curves
low at surface (productivity)
increase to a max at ~1000m
decrease with further depth, then ~stable in deep waters with no more respiration occurring
42
Nitrate characteristics
Bioactive, typical bioactive curve
extra processes not seen in phosphate
controlled by photosynthesis, respiration (dominantly)
43
DIN_preformed
= DIN_T – (r_N:02 x AOU)
44
Nitrogen cycle in the surface
NO3 – NH4 –> (photosyn.) Org N
OrgN – NH4 (respiration)
Org N particle flux out of surface
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nitrogen cycle in the deep
P flux -- Org N to the deep
Org N ––(respiration) NH4 ––(nitrif.) NO3
even deeper, anoxic waters
NO3 / Org N –– N2 (denitrification)
46
N*
DIN – 16DIP
how does [N] differ from the expected P:N ratio?
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+ N*
N is greater than 16P
Nitrogen fixation likely occurring (adding N)
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– N*
N is less than 16P
Denitrification likely occurring, removing N
**must be low O2 waters
49
typical North Atlantic N*
N* +++
high Fe input which is a requirement for N2 fixation
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N* Eastern Equatorial Pacific, Arabian Sea
N* –––
low oxygen zones
51
Preformed nutrients helpful for
separating water masses
52
Denitrification dependent on
O2 only
independent of [N,P]
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AABW
HNLC - high preformed nutrient, low chlorophyl
Fe limited
low CaCO3 precipitation -- high Alk
extremely cold (hence, dense)
54
Atlantic characteristics
N = deep water formation, extremely Saline
~2X S of N Pacific (gulf evaporation)
Generally higher N:P than P
High Fe - Sahara
multiple water sources - AABW, AAIW
harder to see DIC, Alk changes along thermohaline b/c of water mass intrusions
55
AAIW
warmer, less dense than AABW, NADW
spreads out at ~1000m
56
Alkalinity =
[HCO3-] + 2[CO3 ^2-] + [B(OH) ^4-] - [H+]
95% of seawater alk =
[HCO3-] + 2[CO3 ^2-]
57
Alkalinity characteristics
measurable, accurate, not affected by T, P, k (gas exchange)
main effects from CaCO3 precipitation/dissolution
more soluble at depth (P, 'easier' to be small ions)
primarily affected by biology
58
AOU down isopycnal
increases (respiration)
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[P] down isopycnal
increased (respired)
60
O2 down isopycnal
decreased (used up in respiration)
61
∆Alk from 1mol CaCO3 dissolution
increased 2mol
62
Alkalinity profiles
Atlantic- roughly constant with depth, S Atl is higher
Antarctic - roughly constant
Pacific, Indian - increases with depth (thermoh.)
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Pacific characteristics
higher DIP, DIN, DIC, Alk than Atl (more productivity, ventilation)
Deep P_pre ~uniform, 1 water mass
lower [CO3 ^2-], pH
higher fCO2
64
DIC =
[CO2] + [H2CO3] + [HCO3-] + [CO3 ^2-]
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Bicarbonate system
CO2atmos ⇌ CO2ocean ⇌ H2CO3 ⇌ HCO3- ⇌ CO3^2-
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pH =
-log[H+]
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fCO2 =
[CO2] / K
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estimating change in carbonate
∆Alk - ∆DIC ≈ ∆[CO3 ^2-]
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increase in DIC, constant Alk
decrease in CO3 ^2-
decrease in pH
increase in fCO2
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salinity normalized DIC
= (DIC / S) * 35
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Increased Alk, constant DIC
bigger ∆Alk – ∆DIC
higher [CO3 ^2-]
higher pH
lower fCO2
less atmospheric CO2
72
Biologic pump
particle flux
relating biological processes, [nutrient], DIC, Alk
73
P:N:DIC:Alk
dependent on OM:CaCO3, using 3.5
1:16:136:44
74
∆Alk from 1mol Organic Matter respiration
decrease 16/106mol
decrease 0.15mol
75
∆DIC from 1mol CaCO3 dissolution
increase 1mol
76
O2 profile Atlantic vs. Pacific
Pac- much lower concentration at minimum (higher productivity)
deeper, longer O2 minimum
77
pH changes with constant DIC, varying Alk
increase Alk = increase pH
non linear
78
∆DIC from 1mol OM respiration
1mol increase
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CO3 ^2- changes with constant DIC, varying Alk
increase Alk = increase CO3 2-
~linear
80
change in fCO2 with varying Alk, DIC constant
increase Alk = decrease fCO2
non-linear
81
AOU profiles, Atlantic vs. Pacific
Pac. - deeper, longer, higher max, correlates w/ O2 profile
higher productivity
82
pH changes with varying DIC, Alk constant
increase DIC = decrease pH
Alk - DIC is smaller
non linear
83
CO3 2- change with varying DIC, alk constant
Increased DIC = decreased CO3 2-
84
fCO2 change with varying DIC, alk constant
increased DIC = increased fCO2
non-linear
85