I am not copying the whole paper here but it underlines what I havecome to conclude myself. That the driving force for changes in theheat flux into the Arctic is a tidal pulse in the AntarcticCircumpolar Current. This explanation is both simple, persistent andprofoundly elegant.
It is also reasonable that this tidal effect will have a comparableeffect on the opposite side of the globe and thus we likely havespecific local effects at the nine hundred year mark also. In anycase, we have a choke point in the South Atlantic that is affected atleast every 1800 years and reasonably every 900 years which prettyclosely reflects the apparent rough 1100 year cycle suggested by thedata at hand. What the data really reflects is that the data doeshave a cycle that spans centuries. Having a natural tidal cycleallows us to understand that the data presented is a shift in thedistribution curve.
At present we are getting more heat and this allows ice loss to runalong in a variable fashion. When this heat is shut off, the reversewill occur. The data itself at any point will be confusing andmisleading.
At present the tide is in and conditions are warming. This shouldlast a while. My best estimate is around one additional century.
The 1,800-yearoceanic tidal cycle: A possible cause of rapid climate change
Charles D. Keeling*and Timothy P. Whorf
Scripps Institution ofOceanography, University of California, San Diego, La Jolla, CA92093-0244Contributed by CharlesD. Keeling, February 2, 2000
http://www.pnas.org/content/97/8/3814.full.pdf
Variations in solarirradiance are widely believed to explain climatic change on 20,000-to 100,000-year time-scales in accordance with the Milankovitchtheory of the ice ages, but there is no conclusiveevidence that variableirradiance can be the cause of abrupt fluctuations in climate ontime-scales as short as 1,000 years. We propose that such abruptmillennial changes, seen in ice and sedimentary core records, wereproduced in part by well characterized, almost periodic variations inthe strength of the global oceanic tide-raising forces caused byresonances in the periodic motions of the earth and moon. A wellde�ned 1,800-year tidal cycle is associated with gradually shiftinglunar declination fromone episode ofmaximum tidal forcing on the centennial time-scale to the next. Anamplitude modulation of this cycle occurs with an average period ofabout 5,000 years, associated with graduallyshiftingseparation-intervals between perihelion and syzygy at maxima of the1,800-year cycle. We propose that strong tidal forcing causescooling at the sea surface by increasing vertical mixing in theoceans. On the millennial time-scale, this tidal hypothesis issupported by �ndings, from sedimentary records of ice-raftingdebris, that ocean waters cooled close to the times predicted forstrong tidal forcing.
High resolutionice-core and deep-sea sediment-core records over the past millionyears show evidence of abrupt changes in climate superimposed on slowalternations of ice-ages and interglacial warm periods. In generalthese abrupt changes are spaced irregularly, but a distinct subset ofrecurring cold periods, on the millennial time-scale, appears to bealmost periodic. Such events, however, are not clearly apparent inice-core data after the termination of the most recent glaciation,about eleven thousand years (11 kyr) BP (kyr before A.D. 2000). Thisabsence of recent events has led to the hypothesis that theirunderlying cause is related to internal ice-sheet dynamics (ref. 1,p. 35).
Interpretations ofsediment-cores by Bond et al. (1, 2) indicate, however, that a 1- to2-kyr periodicity persisted almost to the present, characterized bydistinct cooling events, including the Little Ice Age that climaxednear A.D. 1600. Although evidence that cooling was more intenseduring glacial times may be explained by some aspect of ice-dynamics,a continuation of cooling events throughout the postglacial Holoceneera suggests an alternative underlying mechanism.
The 1- to 2-kyrIce-Rafted Debris (IRD) Cycle. In a comprehensive comparison ofice-core and sediment-core data, Bond et al. (1) found persistentepisodic cooling events recorded as increases in the amounts of IRDin deep sea sediments of the North Atlantic Ocean basin over the past80 kyr. Consistent periodicity was demonstrated by averaging thetimes between inferred cool events over 12-kyr time intervals. This‘‘pacing’’ of events was found to be restricted to a narrowrange between 1,328 and 1,795 years, with a grand average of 1,476 6585 yr, that they termed a ‘‘1–2 kyr climate cycle.’’
Similar to theseoceanic cooling events, but less frequent and regular, are DansgaardyOeschger events seen in 18Oy16O data of glacial ice. Although suddenwarming events are more conspicuous, these data also show coolingevents. Bond et al. (1) found that Dansgaardy Oeschger cooling eventscoincide with nearly every IRD event during Stage 3 of the lastglaciation when DansgaardyOeschger events were best developed (ref.1, p. 51).
They also found thatHeinrich events, massive discharges of icebergs at intervals of 6–9kyr in the North Atlantic Ocean, were in most cases preceded by IRDevents by 0.5 and 1 kyr (ref. 1,p. 48), suggesting a close linkbetween the two phenomena.
Bond et al. (1)proposed ‘‘that the millennial scale climate variabilitydocumented in Greenland ice cores and North Atlantic sedimentsthrough the last glaciation was not forced by ice sheetinstabilities, but instead arose through modulation of a pervasive1–2 kyr cycle. The persistence of the cycle throughvirtually the entire80 kyr record points to a single forcing mechanism that operatedindependently of the glacia linterglacial climate states’’ (ref.1, p. 55). They did not, however, propose a specific mechanism.
The IRD eventsidentified by Bond et al. (1, 2) show high spectral power density ina broad band centered at about 1,800 years (0.55 6 0.15 cyclesykyr).The authors do not explain why this period is so much larger than the1,476-year average pacing of cool events, but the time-distributionof pacing (ref. 1, Fig. 6C; G. Bond, private communication) suggeststhat a majority of the events were about 2,000 years apart, withoccasional additional events occurring about half-way between,evidently too infrequent to cancel out a dominant spectral peak near1,800 years.
Bond et al. (2) inaddition found a spectral peak near 5,000 years whose possible causewas also not explained. We now propose an oceanic tidal mechanismthat may explain the basis for both of these spectral peaks,consistent with the actual times of IRD events.
A Proposed TidalMechanism for Periodic Oceanic Cooling. In a previous study (3) weproposed a tidal mechanism to explain approximately 6- and 9-yearoscillations in global surface temperature, discernable inmeteorological and oceanographic observations. We first brieflyrestate this mechanism.
The reader is referredto our earlier presentation for more details. We then invoke thismechanism in an attempt to explain millennial variations intemperature.
We propose thatvariations in the strength of oceanic tides cause periodic cooling ofsurface ocean water by modulating the intensity of vertical mixingthat brings to the surface colder water from below. The tides providemore than half of the total power for vertical mixing, 3.5 terawatts(4), compared with about 2.0 terawatts from wind drag (3), makingthis hypothesis plausible.
Moreover, the tidalmixing process is strongly nonlinear, so that vertical mixing causedby tidal forcing must vary in intensity interannually even though theannual rate of power generation is constant (3). As a consequence,periodicities in strong forcing, that we will now characterize byidentifying the peak forcing
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