BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Anthropogenic carbon estimates in the oceanic carbon cycle - Tobia
  Tudino\, University of Exeter
DTSTART:20171101T110000Z
DTEND:20171101T120000Z
UID:TALK85181@talks.cam.ac.uk
CONTACT:Dr Peter Davis
DESCRIPTION:Since 1860\, the atmospheric CO2 has increased from 275 ppm to
  over 400 ppm\, strongly enhancing the associated greenhouse effect. The g
 lobal ocean has mitigated the impacts\, sequestering around a third of the
  human emitted carbon dioxide\, with the highest uptake of anthropogenic C
 O2 (*Cant*) occurring in the Southern Ocean and North Atlantic. However\, 
 oceanic *Cant* cannot be measured directly\, being generally inferred by u
 sing indirect methods with a nominal range of uncertainties included betwe
 en ±10% and ±20%. To better constraint these estimates\, I focus on the 
 North Atlantic Mode waters as they store the largest amount of *Cant* per 
 unit area. In these water masses\, the transit time distribution (TTD) giv
 es the lowest *Cant* while the ∆C gives the highest estimate\, so I conc
 entrate on these two techniques. For both\, a total uncertainty higher tha
 n previously suggested is quantified\, reducing the level of *Cant* confid
 ence to ±29 - 31%. However\, the *Cant* range of uncertainties depends on
  regions\, datasets\, and timeframes: between 1992 and 2010\, observations
  allow to reliably decrease it to ±13 - 15% in the subtropical North Atla
 ntic (20 - 30◦N). Here\, the Mode waters *Cant* content increases at +0.
 5 (TTD) and +0.8 (∆C) ± 0.2μmol kg−1 yr−1\, thus the anthropogenic
  carbon estimates diverge over time. This divergence is ascribable to unst
 eadiness in the air-to-sea CO2 disequilibrium (+0.7 ± 0.2μmol kg−1 yr
 −1)\, and biogeochemical changes\, as suggested by the increasing (+0.3
 μmol kg−1 yr−1) dissolved inorganic carbon from remineralised soft-ti
 ssue: both alterations are unequally captured by the TTD and the ∆C tech
 niques. Changes in the ocean biogeochemistry are further explored using th
 e output of a CM2Mc control simulation over 2kyr. I attribute the accumula
 tion of remineralised carbon to increasing surface productivity (18%)\, de
 creasing wind stress curl (13%)\, weakening meridional mass stream functio
 n (22%)\, hence increasing water mass mean residence time (86%). Ocean aci
 dification additionally alters (68%) and it is influenced by the remineral
 isation increase\, potentially shifting the oceanic carbon cycle towards n
 ew equilibria\, and building a stronger North Atlantic carbon sink than pr
 eviously thought.\n\nTurning attention to the Southern Ocean\, three quest
 ions remain open: (1) how accurate is the estimation of anthropogenic carb
 on in this basin? (2) Is our understanding of the Southern Ocean anthropog
 enic carbon pool impacting on other components of the carbon cycle (e.g. p
 H)? (3) Are our predictions of the future Southern Ocean carbon uptake and
  associated climate change reliable?
LOCATION:British Antarctic Survey\, Innovation Centre\, Seminar Room 307
END:VEVENT
END:VCALENDAR