Chemical Oceanography Flashcards
P:N:C:O2
1:16:106:153
Nitrate
NO3 ^-
Phosphate
PO4 ^ 3-
ocean circulation
~1000yrs
least reactive major ion
Cl-
main barrier to ocean mixing
density difference (hence 2 box model)
Ammonia
NH4+
Average mix layer
~70m
Anoxic waters have
higher burial (recall fish farming)
Largest inputs and outputs
mixing and particle flux»_space; river input, burial
(–) AOU
supersaturation
Nitrite
NO2-
In a CaCO3 dominant system
surface has decreased Alk, decreased [CO3 2-] pH lower fCO2 higher atm CO2 higher
NH4 comes from
respiration product
what happens to NH4 in surface
converted to NO2, NO3 (only in aerobic/oxic zone)
local surface max in NH4
lag in the conversion from
respiration –– NH4+ –– NO2- –– NO3-
Nitrification
NH4 + O2 –– NO2- –– NO3-
Nitrogen Fixation
N2 ––– NH4+
N2 gas from the atmosphere
requires high Fe
expected NH4+ profile
low [ ] in surface water - possible small max from respiration
major increase is after o-a boundary
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
Expected NO2- profile
similar to NO3- but much smaller peak
small peak in oxygen layer from nitrification processes
high N2
denitrification
Conservative ions
only affected by evaporation and precipitation
no big fluctuations with depth
[ion] : seawater S remains ~constant
Mg, Na, Ca, Cl-
Gases
affected by T, S, P, f, reactivity
increase with depth (lower T), except O2
Bioactive elements
affected by primary production, respiration, remineralization
P, N, Fe, O2
Trace metals
Very low concentrations
Mg, Fe, Co, Ni, Cu, Zn, Cd
Oxygen profile without biology
controlled by T like other gases
increase with depth
Oxygen along thermohaline
depleted
successive losses from respiration
AOU
[O2]equil –[O2]meas Apparent Oxygen Utilization amount respired oxygen deficit due to respiration ~ opposite to oxygen curve
typical O2 profile
minimum above 1000m (respiration)
increase after 1000m (horizontal advection from O2 rich high latitude (cold) waters)
Ventilation impact on O2, AOU
larger ventilation (age, older)
lower O2
higher AOU
OUR
Oxygen Utilization Rate
mean respiration rate in the water parcel since it left the surface
AOU / Age
high at surface, decrease with depth
AOU profile
low at surface
max at O2 min (~500-1000m)
decrease with depth
Oxygen minimum occurs
medium age
medium respiration
Carbonate weathering reactions
CaCO3 + CO2 + H2O ––Ca2+ + 2HCO3-
2HCO3- + Ca2+ ––CaCO3 + CO2 + H2O
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
high [surface nutrients], fCO2
high DIC = high fCO2
Phosphate characteristics
enriched along thermohaline
bioactive, typical bioactive curve
high in S ocean (HNLC)
controlled by photosynthesis and respiration
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
DIP respired
= AOU x (P/O2)
i.e. r_P:O2 x AOU
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
Nitrate characteristics
Bioactive, typical bioactive curve
extra processes not seen in phosphate
controlled by photosynthesis, respiration (dominantly)
DIN_preformed
= DIN_T –(r_N:02 x AOU)
Nitrogen cycle in the surface
NO3 – NH4 –> (photosyn.) Org N
OrgN – NH4 (respiration)
Org N particle flux out of surface
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)
N*
DIN –16DIP
how does [N] differ from the expected P:N ratio?
+ N*
N is greater than 16P
Nitrogen fixation likely occurring (adding N)
– N*
N is less than 16P
Denitrification likely occurring, removing N
**must be low O2 waters
typical North Atlantic N*
N* +++
high Fe input which is a requirement for N2 fixation
N* Eastern Equatorial Pacific, Arabian Sea
N* –––
low oxygen zones
Preformed nutrients helpful for
separating water masses
Denitrification dependent on
O2 only
independent of [N,P]
AABW
HNLC - high preformed nutrient, low chlorophyl
Fe limited
low CaCO3 precipitation – high Alk
extremely cold (hence, dense)
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
AAIW
warmer, less dense than AABW, NADW
spreads out at ~1000m
Alkalinity =
[HCO3-] + 2[CO3 ^2-] + [B(OH) ^4-] - [H+]
95% of seawater alk =
[HCO3-] + 2[CO3 ^2-]
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
AOU down isopycnal
increases (respiration)
[P] down isopycnal
increased (respired)
O2 down isopycnal
decreased (used up in respiration)
∆Alk from 1mol CaCO3 dissolution
increased 2mol
Alkalinity profiles
Atlantic- roughly constant with depth, S Atl is higher
Antarctic - roughly constant
Pacific, Indian - increases with depth (thermoh.)
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
DIC =
[CO2] + [H2CO3] + [HCO3-] + [CO3 ^2-]
Bicarbonate system
CO2atmos ⇌ CO2ocean ⇌ H2CO3 ⇌ HCO3- ⇌ CO3^2-
pH =
-log[H+]
fCO2 =
[CO2] / K
estimating change in carbonate
∆Alk - ∆DIC ≈ ∆[CO3 ^2-]
increase in DIC, constant Alk
decrease in CO3 ^2-
decrease in pH
increase in fCO2
salinity normalized DIC
= (DIC / S) * 35
Increased Alk, constant DIC
bigger ∆Alk – ∆DIC higher [CO3 ^2-] higher pH lower fCO2 less atmospheric CO2
Biologic pump
particle flux
relating biological processes, [nutrient], DIC, Alk
P:N:DIC:Alk
dependent on OM:CaCO3, using 3.5
1:16:136:44
∆Alk from 1mol Organic Matter respiration
decrease 16/106mol
decrease 0.15mol
∆DIC from 1mol CaCO3 dissolution
increase 1mol
O2 profile Atlantic vs. Pacific
Pac- much lower concentration at minimum (higher productivity)
deeper, longer O2 minimum
pH changes with constant DIC, varying Alk
increase Alk = increase pH
non linear
∆DIC from 1mol OM respiration
1mol increase
CO3 ^2- changes with constant DIC, varying Alk
increase Alk = increase CO3 2-
~linear
change in fCO2 with varying Alk, DIC constant
increase Alk = decrease fCO2
non-linear
AOU profiles, Atlantic vs. Pacific
Pac. - deeper, longer, higher max, correlates w/ O2 profile
higher productivity
pH changes with varying DIC, Alk constant
increase DIC = decrease pH
Alk - DIC is smaller
non linear
CO3 2- change with varying DIC, alk constant
Increased DIC = decreased CO3 2-
fCO2 change with varying DIC, alk constant
increased DIC = increased fCO2
non-linear
Seasonality affects on nutrients
N, P surface concentrations highest in winter, lowest in summer
minimum lags spring phytoplankton blooms
