David Black, Cariaco and Prompt Archiving

David Black and associates have just (Oct 2007) published a new paper showing a reconstruction of SST from Cariaco sediments using Mg-Ca for the period 1221-1990 (thanks to Eduardo Zorita for alerting me to the study.) In this case, I am happily able to report that the relevant data was archived at WDCP contemporary with publication. Black had already archived data from two other important studies (Black et al 1999, Black et al 2004) in a timely fashion. It’s interesting to contrast Black’s exemplary archiving with the abysmal archiving for another new paper on bristlecones by Hughes and Salzer, noted up recently by Rabett (a paper which I’ll try to comment on some time), which uses information some of which has been unarchived for over 25 years – and where no information collected in the past 17 years has been archived.

Black et al 2007 has particular interest for readers here for several reasons. The Cariaco sediments have a high accumulation for ocean sediments (67 cm/kyr for core PL07-73 BC) and have an annual varve. This has a couple of important benefits: (1) dating precision can be achieved; (2) bioturbation is dramatically reduced (accumulation here being nearly an order of magnitude higher than Arabian Sea RC2730 for example). Secondly, Black has now published and archived near-annual results for four different Cariaco proxies: 1) Mg-Ca in Black et al 2007; 2) G Ruber dO18 and G Bulloides dO18 in Black et al 2004; and 3) weight G Bulloides in Black et al 1999. This latter proxy is not exactly the same as percentage G Bulloides used in the Arabian Sea studies of Anderson, Overpeck and Gupta, but it would presumably be pretty close.

It will also be interesting to compare these results to another high-resolution Mg-Ca seriespublished this year by Richey et al 2007, together with dO18, a study commended by Lloyd Keigwin. Richey presented this study at our AGU session – Mann didn’t like it very much. Tamino has complained about this study as well.

Before presenting Black’s discussion, here is my replot of his Mg-Ca data, also showing the earlier dO18 and G Bulloides data – something that arguably should have been done in Black’s paper (but at least he’s provided materials for others to do so quickly.) The first impression is obviously that the series don’t have much of a common signal over the past 1000 years. Given that Mg-Ca and dO18 give pretty interesting and consistent results on an Ice Age scale over the past million years, it’s a little disappointing to say the least that more of a common signal doesn’t emerge here. It’s not just a high-frequency failure: there’s little commonality in the low frequency either. This is also a disquieting result for results where authors purport to obtain “low frequency” correlations between data which is not nearly as well resolved in time as this data.

One other caveat: the Mg-Ca data (top panel) comes from a different (nearby) box core than the dO18 series. Is it possible that the dating is not all that consistent between the two cores? I don’t know.

cariac33.gif
Figure 1. Cariaco sediments. Top – Mg/Ca reconstruction of SST; middle – G Bulloides and G Ruber dO18; bottom – weight G Bulloides.

The correlations between the series are shown in the table below and are disappointing. Black states of tsuch comparisons: them):

A comparison of the Mg/Ca SST record to G. bulloides abundance, a proxy for upwelling and trade wind variability in the Cariaco Basin [Peterson et al., 1991; Black et al., 1999], reveals very little similarity between the two records. In particular, the large SST changes during the end of the MWP, the beginning of the LIA, and the mid to late twentieth century are not associated with corresponding changes in G. bulloides abundance in either PL07-71BC or PL07-73BC. However, Black et al. [1999] noted a nearzero correlation (r = 0.03) between G. bulloides abundance from a different Cariaco Basin core and local SSTs. A comparison of the G. bulloides abundance record from the core used for this study (PL07-73 BC) to instrumental SSTs over the period of instrumental overlap results in a weak, although statistically significant, correlation (r = 0.18, p <0.1).

Table 1. Correlations between different Cariaco High-Resolution Proxies

 

Mg-Ca

dO18 Bulloides

dO18 Ruber

Wgt Bulloides

Mg

1

-0.14

0.04

0.16

O18_bull

-0.14

1

0.09

-0.23

O18_ruber

0.04

0.09

1

-0.06

wt_bull

0.16

-0.23

-0.06

1

From the information in the top panel, Black reported:

On average, twentieth-century temperatures are not the warmest in the entire record, but they do show the largest increase in magnitude and fastest rate of SST change over the last 800 a.

This genuflection towards global warming is certainly not the first thing that an unbiased data analyst would take away from this information and in a way, reminds me of the now quaint genuflections towards Chairman Mao in Zhu (1973). Black observes that this record is relatively exceptional in its detail:

Varved, high deposition rate sediments deposited under anoxic conditions and an abundance of well-preserved microfossils result in one of the few marine records capable of preserving evidence of interannual- to decadal-scale climate variability in the tropical Atlantic.

and undertakes a calibration of the record against instrumental SST – something that hadn’t been to date in the ocean sediment community (due to low resolution).

No one to date has directly compared a downcore Mg/Ca record to historical instrumental data because there are very few areas with sufficiently high sedimentation rates where one can recover nonbioturbated sediments and high fossil foraminifera abundances. Long-term sedimentation rates in the Cariaco Basin are as much 1 m/ka, and sediments have been deposited under anoxic, nonbioturbated conditions for the last 12.6 ka, thus allowing one to compare and calibrate a suite of paleoceanographic proxies against historical instrumental data. …the Mg/Ca data were then compared to March–April–May average SSTs over the period of instrumental overlap (Figure 3a).

He then compares the record to other recent publications (but not to his own earlier results discussed in the graphic above or to the Richey et al 2007 Gulf of Mexico Mg-Ca result disliked by Tamino. Comparanda were:

  • a high-resolution sclerosponge Sr/Ca-derived SST study from Jamaica (20 m below sea level) [Haase-Schramm et al., 2005]
  • a planktic foraminiferal Mg/Ca SST records from just south of the Dry Tortugas in the northern Caribbean [Lund and Curry, 2006]
  • Nyberg et al., 2002, noting a temporal offset between the two records that cannot be explained by age model differences alone near Bermuda. (Nyberg et al is one of the studies in Moberg)
  • a shorter but high resolution coral Sr/Ca record [Goodkin et al., 2005]
  • percent titanium data from Cariaco Basin sediments [Haug et al., 2001], said to show a similar pattern to Mg/Ca SSTs during the LIA but are distinctly different during the MWP. A
  • a terrestrial lake record of gastropod d18O from the Yucatan Peninsula [Hodell et al., 2000] said to show a nearly identical LIA pattern, including a large drop in values at the beginning of the Maunder Minimum and a subsequent increase, but not the same trends during the MWP or the twentieth century

Black also did not take the opportunity to comment on the percentage Arabian Sea G Bulloides series used by Moberg. Below is a plot showing the difference between Black’s series at Cariaco – using well defined varved sediments – and the series by the Overpeck associates in the Arabian Sea. The Arabian Sea version is used in multiproxy reconstructions (Moberg, Juckes), but the Cariaco version is not. Can anyone give me a justification for using one and not the other that would pass even a first-order smell test?

cariac32.gif
Two G Bulloides Versions. Top – Cariaco; bottom – Arabian Sea.

References:

  • David E. Black, Larry C. Peterson, Jonathan T. Overpeck, Alexey Kaplan, Michael N. Evans, Michaele Kashgarian, 1999. Eight Centuries of North Atlantic Ocean Atmosphere Variability, SCIENCE VOL 286 26 NOVEMBER 1999 Data
  • David E. Black, Robert C. Thunell, Alexey Kaplan, Larry C. Peterson, and Eric J. Tappa. 2004. A 2000-year record of Caribbean and tropical North Atlantic hydrographic variability, PALEOCEANOGRAPHY, VOL. 19, PA2022, doi:10.1029/2003PA000982, 2004 Data
  • David E. Black, Matthew A. Abahazi, Robert C. Thunell, Alexey Kaplan, Eric J. Tappa, and Larry C. Peterson, 2007. An 8-century tropical Atlantic SST record from the Cariaco Basin: Baseline variability, twentieth-century warming, and Atlantic hurricane frequency, PALEOCEANOGRAPHY, VOL. 22, PA4204, doi:10.1029/2007PA001427, 2007 Data

18 Comments

  1. Earle Williams
    Posted Oct 30, 2007 at 2:06 PM | Permalink | Reply

    Steve,

    I assume Table 1 has a column on the left with the proxy names in the same order. Could you modify the table to reflect that, or is this exactly as published?

    Thanks,
    Earle

  2. John A
    Posted Oct 30, 2007 at 2:45 PM | Permalink | Reply

    Sweet Jeebus, there are no correlations between the proxies so how can they be measuring the same thing?

  3. Posted Oct 30, 2007 at 3:10 PM | Permalink | Reply

    Can anyone give me a justification for using one and not the other that would pass even a first-order smell test?

    Steve in a sentence can you help me understand the implication here? Is it that AGW enthusiasts are selectively citing data to support AGW because Black’s study shows a decline in the proxy where the Arabian sea shows an increase? How many studies of this proxy are there in all?

    Also – I’m really intrigued with the Beck analysis of actual CO2 measures over the past century+. In your opinion is there good reason to reject all those measures? Some of them?

    Steve: I would encourage you not to bother with the CO2 measurement issue. I don’t have the time or energy to get into it, other than I don’t want to spend bandwidth here on it.

    IMO there is substantial evidence of cherry-picking data versions of course, there’s always a “Good reason”. Look at the posts on the Yamal substitution for a glaring example.

  4. Paul Dennis
    Posted Oct 30, 2007 at 3:12 PM | Permalink | Reply

    #2

    John A,

    The Mg/Ca ratio of foraminifera is a function of temperature at the time of precipitation of the foram exoskeleton. However, the d18O composition depends on both the temperature of precipitation and the oxygen 18 content of the sea water in which the foram is living. The oxygen 18 content of sea water is strongly positively correlated with salinity. It looks as though the Cariaco basin may have salinity fluctuations as well as temperature fluctuations with time.

    A first pass explanation for the lack of correlation between Mg/Ca temperature and d18O might be along the lines that increasing sea temperature is likely accompanied by an increase in salinity. In such a system the decrease in d18O expected in the foram due to temperature will be compensated by the increasing d18O of the sea water in which the foram is growing.

  5. richardT
    Posted Oct 30, 2007 at 3:21 PM | Permalink | Reply

    #2
    Simple, the different proxies are not measuring the same thing.

  6. Steve Moore
    Posted Oct 30, 2007 at 4:30 PM | Permalink | Reply

    A couple of questions:

    Black notes:

    The tropical North Atlantic does not appear to have experienced a pronounced Medieval Warm Period relative to the complete record. However, strong Little Ice Age cooling of as much as 3 °C occurred between A. D. 1525 and 1625. Spring SSTs gradually rose between A. D. 1650 and 1900 followed by a 2.5 °C warming over the twentieth century.

    I don’t see this in the Mg/Ca SST graph above. Are my eyes deceiving me?

    Also, regarding the “magnitude” of the temperature change in the 20th Century: it certainly appears that the slope is steeper, but is the rate significant when compared to the warming leading to the MWP?
    I guess I’ll have to get the data and answer that myself.

  7. John A
    Posted Oct 30, 2007 at 4:36 PM | Permalink | Reply

    Paul Dennis:

    A first pass explanation for the lack of correlation between Mg/Ca temperature and d18O might be along the lines that increasing sea temperature is likely accompanied by an increase in salinity. In such a system the decrease in d18O expected in the foram due to temperature will be compensated by the increasing d18O of the sea water in which the foram is growing.

    So how would one remove the effects of salinity variations over hundreds of years to recover the supposed temperature signal?

  8. Sam Urbinto
    Posted Oct 30, 2007 at 4:49 PM | Permalink | Reply

    Contrast the quick archiving, replicability and such with Ryan Maue’s logical levelheadedness (And Steve’s and Anthony’s and….) Put it up against The Team (and certain visitors here) and how they act.

    Judith plays well with others even when she disagrees. What is the problem with some folks?

    Ah, well.

  9. Steve McIntyre
    Posted Oct 30, 2007 at 5:19 PM | Permalink | Reply

    #6. You appear to be quoting from a presentation to the spring AGU meeting . The final version (Received 29 January 2007; revised 15 June 2007; accepted 14 August 2007; published 25 October 2007.) says:

    The base of the record captures the latter part of the Medieval Warm Period (MWP), approximately A.D. 1200 and 1425, during which spring SSTs gradually cooled by 0.75C. This cooling was followed by more than 1.0C warming between A.D. 1425 and 1500. The Little Ice Age (LIA) is characterized by a pronounced 1.5C SST decrease between A.D. 1500 and 1640, with a particularly steep drop between approximately 1630 and 1640, almost exactly coincident with the beginning of the Maunder Minimum in 1645 [Eddy, 1976]. SSTs gradually rose again until about A.D. 1800, after which temperatures fluctuate around a mean that is slightly cooler than SSTs observed for the late Medieval Warm Period. A brief 0.5C cooling occurred in the late 1800s and early 1900s followed by a strong 1C warming during the twentieth century.

    Pretty big changes in calibration in the course of the paper tho.

  10. Robert Wood
    Posted Oct 30, 2007 at 6:52 PM | Permalink | Reply

    #4 Well, no matter the rationalisation, these correlation figures mean no correlation; any “explanation” is just handwaving hypothesis and needs to be tested.

  11. Steve McIntyre
    Posted Oct 30, 2007 at 8:54 PM | Permalink | Reply

    I’ve re-plotted the figure showing the various Black versions, so that the dO18 is shown most negative on the top in accordance both with Black et al 2004 and standard interpretations of dO18. As you see, this results in a long-term downward trend with low dO18 values in the 20th century. Black’s interpretation:

    The long-term trend in the Globigerinoides ruber d18O record can be explained by two different but equally plausible scenarios. First, the increase in d18O may indicate that tropical summer-fall SSTs have cooled by as much as 2C over the last 2000 years, possibly as a result of a long-term increase in upwelling intensity. Alternately, comparisons to other studies of ITCZ and regional evaporation/precipitation variability suggest that much of the d18O record is influenced by decadal- to centennial-scale variations in the mean annual position of the ITCZ and associated rainfall patterns.

    I have no particular objection to people interpreting lower dO18 values, such as this, in terms of these sort of explanations. My objection lies not with this interpretation, but with the people such as Lonnie Thompson who will seize on upticks in dO18 as evidence of global warming (e.g. the Hockey Stick in Inconvenient Truth.) If dO18 doesn’t work consistently, you can’t just pick series where it goes up.

  12. Molon Labe
    Posted Oct 30, 2007 at 11:52 PM | Permalink | Reply

    “Black states of tsuch comparisons: them):”

    I can’t parse that.

  13. Michael Jankowski
    Posted Oct 31, 2007 at 6:03 AM | Permalink | Reply

    One heck of a spike (looks like just one year) circa 1900 on the Mg/Ca SST plot. I would’ve thought it would bring up the smoothed average more than it did.

  14. Posted Oct 31, 2007 at 6:31 AM | Permalink | Reply

    Re 13: spike circa 1900

    You couldn’t make that circa 1878 could you? Then it matches a spike in HADCRUT3 NH.

    JF

  15. jae
    Posted Oct 31, 2007 at 9:47 AM | Permalink | Reply

    I don’t like tree ring temperature proxies, but maybe they make more sense than this stuff.

  16. Paul Foote
    Posted Oct 31, 2007 at 9:52 AM | Permalink | Reply

    That spike in 1878 coincides with a large volcanic eruption of Rabaul Caldera, Papua New Guinea. http://volcano.und.edu/vwdocs/current_volcs/rabaul/rabaul.html has an impressive picture from space of the amount of debris cloud put out in a more recent eruption of that volcano.

    Great site. Thanks Steve M. and all your helpers and excellent posters.

  17. Dennis Wingo
    Posted Oct 31, 2007 at 6:05 PM | Permalink | Reply

    The Little Ice Age (LIA) is characterized by a pronounced 1.5C SST decrease between A.D. 1500 and 1640, with a particularly steep drop between approximately 1630 and 1640, almost exactly coincident with the beginning of the Maunder Minimum in 1645

    Steve and the group. In regards to high resolution studies of the transition into the Maunder minimum: Are there other records of sufficient resolution regarding this transition period?

  18. Paul Dennis
    Posted Nov 1, 2007 at 1:33 AM | Permalink | Reply

    #7 and #11

    John A and Steve M,

    there’s a lot of arm waving involved when interpreting d18O signals in natural archives. This is because in most cases the system is under-determined in terms of the number of independent parameters measured.

    The foraminiferal data in Cariaco is a good example. The carbonate oxygen isotope thermometer describes the partitioning of oxygen-18 between water and carbonate as a function of precipitation temperature. i.e. If you know the water d18O and the carbonate d18O an assessment of precipitation temperature can be made.

    In most studies the water d18O is not known and therefore it is not possible to make an accurate assessment of temperature. Therefore the interpretation is wrapped up in caveats such as:

    “The long-term trend in the Globigerinoides ruber d18O record can be explained by two different but equally plausible scenarios. First, the increase in d18O may indicate that tropical summer-fall SSTs have cooled by as much as 2C over the last 2000 years, possibly as a result of a long-term increase in upwelling intensity. Alternately, comparisons to other studies of ITCZ and regional evaporation/precipitation variability suggest that much of the d18O record is influenced by decadal- to centennial-scale variations in the mean annual position of the ITCZ and associated rainfall patterns.”

    Tis simply states they can’t unravel the effects of temperature or salinity changes.

    If one accepts that the Mg/Ca signal in forams is dependent on temperature, then one can try to unravel salinity changes using the d18O data.

    With respect to Lonnie Thompson and ice core we’re looking at a different temperature effect. Here Thompson argues that the precipitation temperature is recorded in the d18O of the ice. This is a well known effect in mid-latitudes where the average annual precipitation composition is closely correlated with local temperature. However, it is not the case at all sites, notably low latitudes and in monsoonal systems where an amount effect dominates temperature. Ideally, extensive studies of local precipitation, temperature, weather systems need to be completed in combination with ice core records in order to understand or calibrate the d18O-temperature relationship. This is very rarely done and is a great problem in most studies of this type.

    Steve, you also raised the point anout forams, d18O and ice ages. Here there is a large change in foram d18O composition between ice ages and interglacials. This is not a temperature signal. Rather the forams are recording the increasing d18O composition of the global ocean as isotopically light water is locked up in large ice sheets. Of course this signal is cocordant with temperature proxies on the ice age-interglacial time scale.

    Finally, one may legitimately ask what use is d18O if it can’t record temperature. The answer is that it can given appropriate systems. One is speleothems where it is possible to measure both drip water composition from fluid inclusions and the carbonate composition. The work is difficult and only a few studies have been completed to date. Another is that there are new techniques in oxygen isotope chemistry being developed that have the promise of being a true thermodynamic thermometer. These measure the partitioning of 18O and 13C within a single carbonate phase, that is the preferential binding of 18O to 13C which is temperature dependent.

One Trackback

  1. By The Trouet Ocean Proxies « Climate Audit on Sep 11, 2010 at 10:34 AM

    [...] Black’s 2007 study (a very high resolution study that was promptly archived) – see here here, but also elsewhere. Trouet don’t use Black’s data, but an earlier 2001 data set by [...]

Post a Comment

Required fields are marked *

*
*

Follow

Get every new post delivered to your Inbox.

Join 2,880 other followers

%d bloggers like this: