Thomas Felis

Increased seasonality in Middle East temperatures during the last interglacial period

The last interglacial period (about 125,000 years ago) is thought to have been at least as warm as the present climate. Owing to changes in the Earths orbit around the Sun, it is thought that insolation in the Northern Hemisphere varied more strongly than today on seasonal timescales, which would have led to corresponding changes in the seasonal temperature cycle. Here we present seasonally resolved proxy records using corals from the northernmost Red Sea, which record climate during the last interglacial period, the late Holocene epoch and the present. We find an increased seasonality in the temperature recorded in the last interglacial coral. Today, climate in the northern Red Sea is sensitive to the North Atlantic Oscillation, a climate oscillation that strongly influences winter temperatures and precipitation in the North Atlantic region. From our coral records and simulations with a coupled atmosphere–ocean circulation model, we conclude that a tendency towards the high-index state of the North Atlantic Oscillation during the last interglacial period, which is consistent with European proxy records, contributed to the larger amplitude of the seasonal cycle in the Middle East.

A coral oxygen isotope record from the northern Red Sea documenting NAO, ENSO, and North Pacific teleconnections on Middle East climate variability since the year 1750

A 245-year coral oxygen isotope record from the northern Red Sea (Ras Umm Sidd/Egypt, ∼28°N) in bimonthly resolution is presented. The mean annual coral δ18O signal apparently reflects varying proportions of both sea surface temperature and δ18Oseawater variability. In conjunction with instrumental observations of climate the coral record suggests for interannual and longer timescales that colder periods are accompanied by more arid conditions in the northern Red Sea but increased rainfall in the southeastern Mediterranean, whereas warmer periods are accompanied by decreased rainfall in the latter and less arid conditions in the northern Red Sea. A ∼70-year oscillation of probably North Atlantic origin dominates the coral time series. Interannual to interdecadal variability is correlated with instrumental indices of the North Atlantic Oscillation (NAO), the El Nino-Southern Oscillation (ENSO), and North Pacific climate variability. The results suggest that these modes contributed consistently to Middle East climate variability since at least 1750, preferentially at a period of ∼5.7 years.

Chapter 1 Mediterranean climate variability over the last centuries: A review

Publisher Summary This chapter discusses a necessary task for assessing to which degree the industrial period is unusual against the background of pre-industrial climate variability. It is the reconstruction and interpretation of temporal and spatial patterns of climate in earlier centuries. There are distinct differences in the temporal resolution among the various proxies. Some of the proxy records are annually or even higher resolved and hence record year-by-year patterns of climate in past centuries. Several of the temperature reconstructions reveal that the late twentieth century warmth is unprecedented at hemispheric scales and is explained by anthropogenic, greenhouse gas (GHG) forcing. The chapter discusses the availability and potential of long, homogenized instrumental data, documentary, and natural proxies to reconstruct aspects of past climate at local- to regional-scales within the larger Mediterranean area, which includes climate extremes and the incidence of natural disasters. The chapter describes the role of external forcing, including natural and anthropogenic influences, and natural, internal variability in the coupled ocean–atmosphere system at subcontinental scale.

Subtropical coral reveals abrupt early-twentieth-century freshening in the western North Pacific Ocean

Instrumental climate observations provide robust records of global land and ocean temperatures during the twentieth century. Unlike for temperature, continuous salinity observations in the surface ocean are scarce prior to 1970, and the magnitude of salinity changes during the twentieth century is largely unknown. Surface ocean salinity is a major component in climate dynamics, as it influences ocean circulation and water mass formation. Here we present an annually resolved reconstruction of salinity variations in the surface waters of the western subtropical North Pacific Ocean since 1873, based on bimonthly records of δ18O, Sr/Ca, and U/Ca in a coral from the Ogasawara Islands. The reconstruction indicates that an abrupt regime shift toward fresher surface ocean conditions occurred between 1905 and 1910. Observational atmospheric data suggest that the abrupt freshening was associated with a weakening of the winds that drive the Kuroshio Current system and the associated subtropical gyre circulation. We note that the abrupt early-twentieth-century freshening in the western subtropical North Pacific precedes abrupt climate change in the northern North Atlantic by a few years. The potential for abrupt regime shifts in surface ocean salinity should be considered in climate predictions for the coming decades.

U-series dating of diagenetically altered fossil reef corals☆

Initial (234U/238U) activity ratios higher than those expected from closed system evolution of seawater are an outstanding problem in U-series dating of fossil reef corals. The increased activity ratios are ascribed to post-depositional diagenesis. We analysed six Last Interglacial and one Holocene coral of the genus Porites collected near the northern end of the Gulf of Aqaba (northern Red Sea) together with three recent corals from this location as a modern reference. While the values measured on the recent samples show no deviation from expected values, the Holocene and Last Interglacial corals display highly elevated (234U/238U) activity ratios as well as increased 238U and 232Th concentrations. (234U/238U) activity ratios are strongly correlated with (230Th/238U) and total uranium content. A model assuming different degrees of uranium addition and subsequent loss in different sub-samples of one coral produces straight lines (isochrons) on a (234U/238U)–(230Th/238U) plot and predicts that the true age of the coral can be calculated by intersecting this isochron with the seawater evolution curve. We used the strong correlation detected in the Aqaba corals to calculate isochron ages. The isochron age of the Holocene coral (3116 +167 −156 yr) is concordant with its calibrated 14C age (2963 +92 −103 yr). The ages of the Last Interglacial corals are between 121 (+6.7 −5.3) and 121.9 (+7.0 −6.3) kyr for a higher terrace (7–10 m asl) and 106.4 (+8.9 −8.1) and 117.1 (+19.7 −15.3) kyr for a lower terrace (4–5 m asl). One Last Interglacial coral with an aragonite content of ∼85% could not be dated. The elevation and ages of the fossil terraces are consistent with existing sea level reconstructions from the Red Sea.

A Review of 2000 Years of Paleoclimatic Evidence in the Mediterranean

The integration of climate information from instrumental data and documentary and natural archives; evidence of past human activity derived from historical, paleoecological, and archaeological records; and new climate modeling techniques promises major breakthroughs for our understanding of climate sensitivity, ecological processes, environmental response, and human impact. In this chapter, we review the availability and potential of instrumental data, less well-known written records, and terrestrial and marine natural proxy archives for climate in the Mediterranean region over the last 2000 years. We highlight the need to integrate these different proxy archives and the importance for multiproxy studies of disentangling complex relationships among climate, sea-level changes, fire, vegetation, and forests, as well as land use and other human impacts. Focusing on dating uncertainties, we address seasonality effects and other uncertainties in the different proxy records. We describe known and anticipated challenges posed by integrating multiple diverse proxies in high-resolution climate-variation reconstructions, including proxy limitations to robust reconstruction of the natural range of climate variability and problems specific to temporal scales from interannual to multicentennial. Finally, we highlight the potential of paleo models to contribute to climate reconstructions in the Mediterranean, by narrowing the range of climate-sensitivity estimates and by assimilating multiple proxies.

Arctic Oscillation signature in a Red Sea coral

We show that the winter time series of the Ras Umm Sidd coral oxygen isotope record from the northern Red Sea (approximately 28°N) is linked to the Arctic Oscillation phenomenon, the Northern Hemispheres dominant mode of atmospheric variability. Until now, the detection of this mode, which is most prominent in winter, in proxy climate records was difficult due to the lack of a clear seasonality in most paleoclimatic archives. The results suggest that northern Red Sea corals can provide information about the low-frequency variability of the Northern Hemisphere winter circulation during the pre-instrumental period.

Pronounced interannual variability in tropical South Pacific temperatures during Heinrich Stadial 1

The early last glacial termination was characterized by intense North Atlantic cooling and weak overturning circulation. This interval between ~18,000 and 14,600 years ago, known as Heinrich Stadial 1, was accompanied by a disruption of global climate and has been suggested as a key factor for the termination. However, the response of interannual climate variability in the tropical Pacific (El Niño-Southern Oscillation) to Heinrich Stadial 1 is poorly understood. Here we use Sr/Ca in a fossil Tahiti coral to reconstruct tropical South Pacific sea surface temperature around 15,000 years ago at monthly resolution. Unlike today, interannual South Pacific sea surface temperature variability at typical El Niño-Southern Oscillation periods was pronounced at Tahiti. Our results indicate that the El Niño-Southern Oscillation was active during Heinrich Stadial 1, consistent with climate model simulations of enhanced El Niño-Southern Oscillation variability at that time. Furthermore, a greater El Niño-Southern Oscillation influence in the South Pacific during Heinrich Stadial 1 is suggested, resulting from a southward expansion or shift of El Niño-Southern Oscillation sea surface temperature anomalies.

Shift in ENSO Teleconnections Recorded by a Northern Red Sea Coral

Abstract El Nino–Southern Oscillation (ENSO) teleconnections over Europe and the Middle East are evaluated using an oxygen isotope coral time series from the northern Red Sea and various instrumental datasets. A shift in the correlation between the Nino-3 index and the Red Sea coral record in the 1970s is detected, and it is shown that this shift can be attributed to nonstationary circulation regimes and related ENSO teleconnections. It is found that positive anomalies of oxygen isotope in the Red Sea coral record from the middle 1930s to the late 1960s are associated with a strong Pacific–North Atlantic teleconnection accompanied by a weak Aleutian low, a more zonal flow at midlatitudes, and La Nina conditions in tropical Pacific. In contrast, positive anomalies of oxygen isotopes in the Red Sea coral after the 1970s are related to El Nino conditions and weaker Pan-Pacific–Atlantic circulation regimes. Using the window correlation of the northern Red Sea coral record with two coral records from the tropi...

Climate records from corals

In many regions instrumental climate records are too short to resolve the full range of decadal- to multidecadal-scale natural climate variability. Massive annually banded corals from the tropical and subtropical oceans provide a paleoclimatic archive with a seasonal resolution, documenting past variations in water temperature, hydrologic balance, and ocean circulation. Recent coral-based paleoclimatic research has focused mainly on the tropics, providing important implications on the past variability of the El Nino-Southern Oscillation (ENSO) phenomenon and decadal tropical climate variability. However, new records from some of the rare subtropical/mid-latitude locations of coral growth were shown to reflect aspects of dominant modes of Northern Hemisphere climate variability, e.g. the North Atlantic Oscillation (NAO). This natural mode has important socio-economic impacts owing to its large-scale modulation of droughts, floods, storms, snowfall, and fish stocks at timescales relevant to society. Coral records extending over several centuries from key locations (e.g. northern Red Sea, Bermuda) provide the opportunity to assess recent shifts in the NAO with respect to the natural variability of the pre-instrumental period. Providing a better understanding of NAO dynamics, such paleoclimatic records, together with those derived from other paleoclimatic archives, are essential for the predictability of future European climate.