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Tracking the Atlantic Multidecadal Oscillation through the last 8,000 years.

Knudsen MF, Seidenkrantz MS, Jacobsen BH, Kuijpers A - Nat Commun (2011)

Bottom Line: Understanding the internal ocean variability and its influence on climate is imperative for society.The nature and origin of the AMO is uncertain, and it remains unknown whether it represents a persistent periodic driver in the climate system, or merely a transient feature.We therefore conjecture that a quasi-persistent ∼55- to 70-year AMO, linked to internal ocean-atmosphere variability, existed during large parts of the Holocene.

View Article: PubMed Central - PubMed

Affiliation: Centre for Past Climate Studies, Department of Earth Sciences, Aarhus University, HÃøegh-Guldbergs Gade 2, Aarhus DK-8000, Denmark. mfk@geo.au.dk

ABSTRACT
Understanding the internal ocean variability and its influence on climate is imperative for society. A key aspect concerns the enigmatic Atlantic Multidecadal Oscillation (AMO), a feature defined by a 60- to 90-year variability in North Atlantic sea-surface temperatures. The nature and origin of the AMO is uncertain, and it remains unknown whether it represents a persistent periodic driver in the climate system, or merely a transient feature. Here, we show that distinct, ∼55- to 70-year oscillations characterized the North Atlantic ocean-atmosphere variability over the past 8,000 years. We test and reject the hypothesis that this climate oscillation was directly forced by periodic changes in solar activity. We therefore conjecture that a quasi-persistent ∼55- to 70-year AMO, linked to internal ocean-atmosphere variability, existed during large parts of the Holocene. Our analyses further suggest that the coupling from the AMO to regional climate conditions was modulated by orbitally induced shifts in large-scale ocean-atmosphere circulation.

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Related in: MedlinePlus

Linking Holocene climate records to the AMO index.(a) The Atlantic multidecadal oscillation (AMO) index4 (black) shown together with instrumental records of precipitation variability in the Sahel region (brown) and on the Yucatan peninsula (green; courtesy of the National Meteorological Survey of Mexico). Note that the instrumental precipitation record from the Yucatan peninsula has been inverted, implying that warm (cold) AMO phases correspond to dry (wet) conditions. (b) The AMO index4 (black) and the instrumental precipitation record from the Yucantan peninsula (green) is shown together with the coral-based δ18O record from Puerto Rico14 (red) and the δ18O record from lake Chichancanab29 (dashed green line). Note that the sign of the Chichancanab record (high δ18O=dry) means that warm AMO phases were associated with drier conditions, which is in full agreement with the instrumental record from the Yucatan peninsula and numerical model simulations7. (c) The AMO index4 (black) along with the δ18O records from GRIP24 (magenta) and GISP226 (orange) ice cores. All the records have been detrended and normalized to one standard deviation unit. Nine-year running means were computed for all records with an annual resolution, that is, the instrumental records and the δ18O record from Puerto Rico, whereas 20-year running means were computed for the GRIP and GISP2 δ18O records to suppress short-term δ18O scatter.
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f2: Linking Holocene climate records to the AMO index.(a) The Atlantic multidecadal oscillation (AMO) index4 (black) shown together with instrumental records of precipitation variability in the Sahel region (brown) and on the Yucatan peninsula (green; courtesy of the National Meteorological Survey of Mexico). Note that the instrumental precipitation record from the Yucatan peninsula has been inverted, implying that warm (cold) AMO phases correspond to dry (wet) conditions. (b) The AMO index4 (black) and the instrumental precipitation record from the Yucantan peninsula (green) is shown together with the coral-based δ18O record from Puerto Rico14 (red) and the δ18O record from lake Chichancanab29 (dashed green line). Note that the sign of the Chichancanab record (high δ18O=dry) means that warm AMO phases were associated with drier conditions, which is in full agreement with the instrumental record from the Yucatan peninsula and numerical model simulations7. (c) The AMO index4 (black) along with the δ18O records from GRIP24 (magenta) and GISP226 (orange) ice cores. All the records have been detrended and normalized to one standard deviation unit. Nine-year running means were computed for all records with an annual resolution, that is, the instrumental records and the δ18O record from Puerto Rico, whereas 20-year running means were computed for the GRIP and GISP2 δ18O records to suppress short-term δ18O scatter.

Mentions: Several studies have linked precipitation changes to AMO variability7910, but the coupling between the AMO and precipitation anomalies is spatially complex; a warm AMO phase is thought to be associated with a positive precipitation anomaly in the Sahel region of Africa, whereas precipitation anomalies in, for example, Mexico appear to have been in anti-phase with the AMO and Sahel precipitation7. This is illustrated in Figure 2, which compares the AMO index to instrumental data and climate proxy records from the Atlantic region. Recent model experiments, however, have failed to identify the AMO as the primary driver of recent reductions in Sahel rainfall23. In fact, these model simulations indicate that the major climate impacts of multidecadal changes in Atlantic Ocean SST over land are to be found in North America and the northern part of South America. To investigate the existence and origin of the AMO on Holocene timescales, we carefully selected seven Holocene climate proxy records from the North Atlantic region, including five ice-core records from Greenland24252627 and the Canadian Arctic28, one lacustrine record from the Yucatan peninsula29, Mexico, and a marine record from the Cariaco Basin30, north of Venezuela (Figs 3 and 4). These records derive from sites that are located close to the current summer positions of the atmospheric polar front (PF) or the intertropical convergence zone (ITCZ). The records were chosen based on a their documented sensitivity to variations in North Atlantic SST, and an average temporal resolution of 25 years or better (Supplementary Table S1) over a time span of 8,000 years or more. The majority of these climate proxy records overlap the instrumental AMO record in time, and, although the temporal resolution for some of the proxy records is relatively low for the past 140 years, they clearly tend to co-vary with the AMO index (Fig. 2). The precipitation proxy record from Lake Chichancanab (Yucatan) co-varies with both the AMO index and a coral-based SST reconstruction from Puerto Rico, with the instrumental precipitation record from the Yucatan peninsula looking almost like an extension of the Lake Chichancanab proxy record (Fig. 2b). The comparisons show that warm AMO phases correlate with dry periods on the Yucatan Peninsula, which is in accord with numerical model simulations7 (note that the instrumental rainfall record from Yucantan has been inverted in Fig. 2b, and that high δ18O values from Lake Chichancanab correspond to dry periods). The GRIP record and, in particular, the GISP2 record also co-vary with the AMO index over the last 140 years (Fig. 2c), suggesting that the two ice-core records were sensitive to North Atlantic SST variations, with increasing SST leading to increasing δ18O values as expected. Apart from North Atlantic SST variations, climate variability observed in these proxy records may to some extent also have been driven by other Northern Hemisphere (NH), or even global-scale, climate effects that are correlated with the AMO. The potential existence of such NH teleconnections is underpinned by coupled ocean-atmosphere models520. Irrespective of this ambiguity regarding the principal driving mechanism, it remains very likely that the observed multidecadal variability, be it directly or indirectly, reflects North Atlantic SST variations related to the AMO.


Tracking the Atlantic Multidecadal Oscillation through the last 8,000 years.

Knudsen MF, Seidenkrantz MS, Jacobsen BH, Kuijpers A - Nat Commun (2011)

Linking Holocene climate records to the AMO index.(a) The Atlantic multidecadal oscillation (AMO) index4 (black) shown together with instrumental records of precipitation variability in the Sahel region (brown) and on the Yucatan peninsula (green; courtesy of the National Meteorological Survey of Mexico). Note that the instrumental precipitation record from the Yucatan peninsula has been inverted, implying that warm (cold) AMO phases correspond to dry (wet) conditions. (b) The AMO index4 (black) and the instrumental precipitation record from the Yucantan peninsula (green) is shown together with the coral-based δ18O record from Puerto Rico14 (red) and the δ18O record from lake Chichancanab29 (dashed green line). Note that the sign of the Chichancanab record (high δ18O=dry) means that warm AMO phases were associated with drier conditions, which is in full agreement with the instrumental record from the Yucatan peninsula and numerical model simulations7. (c) The AMO index4 (black) along with the δ18O records from GRIP24 (magenta) and GISP226 (orange) ice cores. All the records have been detrended and normalized to one standard deviation unit. Nine-year running means were computed for all records with an annual resolution, that is, the instrumental records and the δ18O record from Puerto Rico, whereas 20-year running means were computed for the GRIP and GISP2 δ18O records to suppress short-term δ18O scatter.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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f2: Linking Holocene climate records to the AMO index.(a) The Atlantic multidecadal oscillation (AMO) index4 (black) shown together with instrumental records of precipitation variability in the Sahel region (brown) and on the Yucatan peninsula (green; courtesy of the National Meteorological Survey of Mexico). Note that the instrumental precipitation record from the Yucatan peninsula has been inverted, implying that warm (cold) AMO phases correspond to dry (wet) conditions. (b) The AMO index4 (black) and the instrumental precipitation record from the Yucantan peninsula (green) is shown together with the coral-based δ18O record from Puerto Rico14 (red) and the δ18O record from lake Chichancanab29 (dashed green line). Note that the sign of the Chichancanab record (high δ18O=dry) means that warm AMO phases were associated with drier conditions, which is in full agreement with the instrumental record from the Yucatan peninsula and numerical model simulations7. (c) The AMO index4 (black) along with the δ18O records from GRIP24 (magenta) and GISP226 (orange) ice cores. All the records have been detrended and normalized to one standard deviation unit. Nine-year running means were computed for all records with an annual resolution, that is, the instrumental records and the δ18O record from Puerto Rico, whereas 20-year running means were computed for the GRIP and GISP2 δ18O records to suppress short-term δ18O scatter.
Mentions: Several studies have linked precipitation changes to AMO variability7910, but the coupling between the AMO and precipitation anomalies is spatially complex; a warm AMO phase is thought to be associated with a positive precipitation anomaly in the Sahel region of Africa, whereas precipitation anomalies in, for example, Mexico appear to have been in anti-phase with the AMO and Sahel precipitation7. This is illustrated in Figure 2, which compares the AMO index to instrumental data and climate proxy records from the Atlantic region. Recent model experiments, however, have failed to identify the AMO as the primary driver of recent reductions in Sahel rainfall23. In fact, these model simulations indicate that the major climate impacts of multidecadal changes in Atlantic Ocean SST over land are to be found in North America and the northern part of South America. To investigate the existence and origin of the AMO on Holocene timescales, we carefully selected seven Holocene climate proxy records from the North Atlantic region, including five ice-core records from Greenland24252627 and the Canadian Arctic28, one lacustrine record from the Yucatan peninsula29, Mexico, and a marine record from the Cariaco Basin30, north of Venezuela (Figs 3 and 4). These records derive from sites that are located close to the current summer positions of the atmospheric polar front (PF) or the intertropical convergence zone (ITCZ). The records were chosen based on a their documented sensitivity to variations in North Atlantic SST, and an average temporal resolution of 25 years or better (Supplementary Table S1) over a time span of 8,000 years or more. The majority of these climate proxy records overlap the instrumental AMO record in time, and, although the temporal resolution for some of the proxy records is relatively low for the past 140 years, they clearly tend to co-vary with the AMO index (Fig. 2). The precipitation proxy record from Lake Chichancanab (Yucatan) co-varies with both the AMO index and a coral-based SST reconstruction from Puerto Rico, with the instrumental precipitation record from the Yucatan peninsula looking almost like an extension of the Lake Chichancanab proxy record (Fig. 2b). The comparisons show that warm AMO phases correlate with dry periods on the Yucatan Peninsula, which is in accord with numerical model simulations7 (note that the instrumental rainfall record from Yucantan has been inverted in Fig. 2b, and that high δ18O values from Lake Chichancanab correspond to dry periods). The GRIP record and, in particular, the GISP2 record also co-vary with the AMO index over the last 140 years (Fig. 2c), suggesting that the two ice-core records were sensitive to North Atlantic SST variations, with increasing SST leading to increasing δ18O values as expected. Apart from North Atlantic SST variations, climate variability observed in these proxy records may to some extent also have been driven by other Northern Hemisphere (NH), or even global-scale, climate effects that are correlated with the AMO. The potential existence of such NH teleconnections is underpinned by coupled ocean-atmosphere models520. Irrespective of this ambiguity regarding the principal driving mechanism, it remains very likely that the observed multidecadal variability, be it directly or indirectly, reflects North Atlantic SST variations related to the AMO.

Bottom Line: Understanding the internal ocean variability and its influence on climate is imperative for society.The nature and origin of the AMO is uncertain, and it remains unknown whether it represents a persistent periodic driver in the climate system, or merely a transient feature.We therefore conjecture that a quasi-persistent ∼55- to 70-year AMO, linked to internal ocean-atmosphere variability, existed during large parts of the Holocene.

View Article: PubMed Central - PubMed

Affiliation: Centre for Past Climate Studies, Department of Earth Sciences, Aarhus University, HÃøegh-Guldbergs Gade 2, Aarhus DK-8000, Denmark. mfk@geo.au.dk

ABSTRACT
Understanding the internal ocean variability and its influence on climate is imperative for society. A key aspect concerns the enigmatic Atlantic Multidecadal Oscillation (AMO), a feature defined by a 60- to 90-year variability in North Atlantic sea-surface temperatures. The nature and origin of the AMO is uncertain, and it remains unknown whether it represents a persistent periodic driver in the climate system, or merely a transient feature. Here, we show that distinct, ∼55- to 70-year oscillations characterized the North Atlantic ocean-atmosphere variability over the past 8,000 years. We test and reject the hypothesis that this climate oscillation was directly forced by periodic changes in solar activity. We therefore conjecture that a quasi-persistent ∼55- to 70-year AMO, linked to internal ocean-atmosphere variability, existed during large parts of the Holocene. Our analyses further suggest that the coupling from the AMO to regional climate conditions was modulated by orbitally induced shifts in large-scale ocean-atmosphere circulation.

Show MeSH
Related in: MedlinePlus