Evolution of North Atlantic ventilation

1
Evolution of North Atlantic ventilation
Similar to today
Robinson et al. 2005 Science
2
Dansgaard-Oeschger cycles
Not shown are data from benthic forams and other
proxies that indicate cold events within D-O
cycles are associated with MOC/THC change. This
relationship is the basis for concern that
similar abrupt changes could occur today.
3
Hulu Cave D-O cycles
D-O cycles are widespread and synchronous at many
locations around the globe
4
IS-12 and -14 on Blake Ridge
5
Paleosalinity
IS12
IS14
Warm, fresh
Low d18-O during IS-12 and -14 mostly reflects
some combination of high SST and low SSS
Cold, salty
Warm
SST can be calculated from Mg/Ca measurements in
the same forams as d18-O
Cold
fresh
The SST effect can be removed from foram d18-O to
give the d18-O of seawater. This is a function
of salinity
salty
(after Schmidt et al. 2006)
6
Increased SSS during LIA
Nyland et al. 2006
Keigwin 1996

Hendy et al. 2002
Lund and Curry 2006

Hodell et al. 2005




Saenger thesis work

Haug et al. 2003
7
.
Bermuda Rise
X
8
More NADW during LIA
More NADW during the LIA is opposite what we
would expect based on behavior of D-O cycles
during the glacial epoch. The difference between
the two situations may be the extent of ice
sheets. It is consistent with higher SSS in the
western North Atlantic. We now have data from a
core north of the Gulf Stream that supports the
Bermuda Rise observation. Abrupt climate
changes observed in paleo data during the late
Holocene are relatively small, but would still
have large societal impact.
Core top -127
Note we assume N and S end members of -40 and
-140 , respectively. These differ from the end
members used by Broecker (-67 and -160 ).
(Keigwin and Guilderson, unpubl.)
9
NERC Rapid Climate Change (RAPID) programme

• 20M (2001-2008) 36 projects funded
• 1st AO MOC AO 2002, 2nd AO and joint
  international AO 2003
• Internationally, working with NSF and NOAA (USA,
  7M shiptime Florida Strait cable
  measurements), RCN (Norway, 1M), NWO
  (Netherlands,1.5M), plus informal links with
  Germany
• In UK, working with Hadley Centre and many others
  (policy links to DEFRA)
• Web page - http//rapid.nerc.ac.uk/

10
RAPID - aims

• RAPID aims to investigate and understand the
  causes of rapid climate change, with a main (but
  not exclusive) focus on the role of the Atlantic
  Oceans Thermohaline Circulation (THC)

n.b. in practice we can observe the meridional
overturning circulation (MOC) rather than the THC
11
RAPID MOC observing system

• 26.5N array
• WAVE array

12
RAPID 26.5N array 2004/5
13
The future RAPID-WATCH

• RAPID-WATCH (Will the Atlantic Thermohaline
  Circulation Halt) proposal for period 2007-2014
• Currently under consideration by NERC
• Outline bid approved by NERC autumn 2005
• Full bid submitted Easter 2006
• Reviews and responses summer 2006
• Decision by NERC before the end of 2006
• Being done in concert with the NERC marine labs
  Oceans 2025 bid (their funding proposal for
  period 2007-2012)
• Continuing cooperation with international partners

14
RAPID-WATCH objectives

• To deliver a decade-long time series of
  calibrated and quality-controlled measurements of
  the Atlantic MOC from the RAPID-WATCH arrays
• To exploit the data from the RAPID-WATCH arrays
  and elsewhere to determine and interpret recent
  changes in the Atlantic MOC, assess the risk of
  rapid climate change, and investigate the
  potential for predictions of the MOC and its
  impacts on climate

15
Conclusions

• Recent developments in paleoceanography indicate
  the role of salinity in climate change may be
  larger than we thought. Because we know salinity
  has been changing for decades in the North
  Atlantic region, salinity should be monitored in
  the modern ocean as part of any observing system.
  The record of climate change during recent
  millennia suggests different forcing than during
  the ice age. Holocene climate needs focused
  study (especially the past 6 kyr).
• Any early warning system for abrupt climate
  change should coordinate with major European
  efforts that are already underway.
• Although the paleo record indicates huge climate
  changes can occur within a decade, if they are to
  occur at all in the next century it may be
  decades from now. We need to study the recent
  geological past now because we cannot afford to
  wait decades to catch an abrupt change in real
  time.
• As with the U.K. RAPID Program, any U.S. program
  should monitor the atmosphere, the ocean, the
  cryosphere, and recent millennia of proxy data.