Norel Rimbu

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.

Orbitally driven insolation forcing on Holocene climate trends: Evidence from alkenone data and climate modeling

A global spatial pattern of long-term sea surface temperature (SST) trends over the last 7000 years is explored using a comparison of alkenone-derived SST records with transient ensemble climate simulations with a coupled atmosphere-ocean circulation model under orbitally driven insolation forcing. The spatial trend pattern both in paleo-SST data and in model results shows pronounced global heterogeneity. Generally, the extratropics cooled while the tropics experienced a warming during the middle to late Holocene. We attribute these divergent Holocene climate trends to seasonally opposing insolation changes. Furthermore, climate mode changes similar to the Arctic/North Atlantic Oscillation are superimposed on the prevalent pattern. It is concluded that nonlinear changes in the entire seasonal cycle of insolation played a dominant role for the temporal evolution of Holocene surface temperatures. For understanding of marine proxy data, apart from the dominance of summer insolation in high latitudes, a notable shift in the maximum insolation of the year in low latitudes has to be taken into account, which may influence timing of phytoplankton production and thus alters the seasonal origin of temperature signals recorded in the proxies.

Impacts of the North Atlantic gyre circulation on Holocene climate off northwest Africa

We present well-dated high-resolution Holocene records of sea-surface temperature (SST) and upwelling intensity off northwest (NW) Africa. We identify long-term cooling trends over the Holocene in the subtropical North Atlantic in response to boreal summer insolation. A pronounced cooling event of similar to 1 degrees C ca. 8.5 cal ka indicates a large-scale reorganization of the ocean current system possibly induced by meltwater from the northern North Atlantic. Our alkenone SST record off Cape Ghir provides strong evidence for the impact of ocean circulation changes on subtropical North Atlantic SSTs. It is likely that cold waters were propagated to the subtropics via the Canary Current in a way similar to Heinrich events and the Younger Dryas off Cape Blanc. We find 2-3 k.y. periodic variations in SST and upwelling intensity off NW Africa superimposed on the cooling trend. Such a cycle has been documented in various paleoclimate archives in phase with solar forcing. We show that these variations on millennial time scales are linked to the North Atlantic subtropical gyre circulation and the Northern Hemisphere atmospheric circulation, and in particular to changes in the pressure gradient between the Icelandic Low and the Azores High. This suggests that oceanic circulation, in response to solar forcing, played a more important role in the generation of 2-3 k.y. cyclicity than has been previously considered.

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.

Impacts of the North Atlantic Oscillation and the El Niño–Southern Oscillation on Danube river flow variability

The impact of the North Atlantic Oscillation (NAO) and El Nino-Southern Oscillation (ENSO) on the Danube river streamflow variability is investigated for the period 1840 to 1998. A composite analysis reveals that positive streamflow anomalies are related to a large scale atmospheric circulation pattern that contains elements of the positive phase of the Pacific North American (PNA) pattern and negative phase of the NAO. The corresponding sea surface temperature (SST) pattern shows positive anomalies over most of the tropical region. Opposite atmospheric circulation and SST patterns are associated to negative streamflow anomalies. Significant decadal variations of the NAO and ENSO impact on the Danube streamflow are detected for the observational period. A lag-correlation analysis reveals that winter SST from tropical Pacific and some regions from the North Atlantic are significantly correlated with the streamflow variations from spring and summer suggesting a possible predictive skill of the Danube streamflow anomalies in these seasons using winter SST as a predictor.

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...

Prediction of Spring Elbe Discharge Based on Stable Teleconnections with Winter Global Temperature and Precipitation

Abstract The predictability of Elbe streamflow anomalies during spring is examined using previous winter sea surface temperature (SST), temperature over land (TT), and precipitation (PP) anomalies. Based on running correlation analysis, the authors identify several regions where the spring streamflow anomalies are stable correlated with SST, TT, and PP anomalies from the previous winter. During the period 1902–71 the Elbe spring streamflow is stable correlated with previous winter PP anomalies from its catchment area, with TT anomalies from the Black Sea–Caspian Sea region, northwestern Europe, and northern Canada as well as with SST anomalies from the tropical Pacific, the Indian Ocean, and several regions of the North Pacific and the North Atlantic. An index based on winter SST, TT, and PP anomalies from these regions is highly significantly correlated with spring streamflow anomalies during this period. Based on SST, TT, and PP anomalies from stable correlated regions, a forecast scheme is developed an...

Multidecadal variability of summer temperature over Romania and its relation with Atlantic Multidecadal Oscillation

We investigate the multidecadal variability of summer temperature over Romania as measured at 14 meteorological stations with long-term observational records. The dominant pattern of summer temperature variability has a monopolar structure and shows pronounced multidecadal variations. A correlation analysis reveals that these multidecadal variations are related with multidecadal variations in the frequency of four daily atmospheric circulation patterns from the North Atlantic region. It is found that on multidecadal time scales, negative summer mean temperature (TT) anomalies are associated with positive sea level pressure (SLP) anomalies centered over the northern part of the Atlantic Ocean and Scandinavia and negative SLP anomalies centered over the northern part of Africa. It is speculated that a possible cause of multidecadal fluctuations in the frequency of these four patterns are the sea surface temperature (SST) anomalies associated to the Atlantic Multidecadal Oscillation (AMO). These results have implications for predicting the evolution of summer temperature over Romania on multidecadal time scales.

Quasi-Decadal Variability in the Atlantic Basin Involving Tropics–Midlatitudes and Ocean–Atmosphere Interactions

Observational data are used to emphasise a 5- to 7-yr lag between the main modes of variability in the midlatitudes and in the Tropics. Considering this finding a mechanism for quasidecadal variability based on Tropics‐midlatitudes and ocean‐atmosphere interaction is described. It appears that the signal associated with the SST anomalies in the northern region of the tropical Atlantic is transferred in midlatitudes through the atmosphere and it will modify the thermal conditions of the ocean upper layers. In 5‐7 years, thermal conditions will affect the SST anomalies in the northern Tropics reversing their sign. The results suggest that the Tropics get a negative feedback from midlatitudes so that the Tropics‐midlatitudes system is capable of generating an oscillatory mode.

Interannual Variability of Rhine River Streamflow and Its Relationship with Large-Scale Anomaly Patterns in Spring and Autumn

AbstractInterannual-to-decadal variability of Rhine River streamflow and their relationship with large-scale climate anomaly patterns for spring [March–May (MAM)] and autumn [September–November (SON)] are investigated through a statistical analysis of observed streamflow data and global climate anomaly fields. A wavelet analysis reveals that spring streamflow variability is nonstationary with enhanced variability in the 8–16-yr band from 1860 to 1900 and in the 2–8 and 16–30 yr after 1960. A composite analysis reveals that streamflow anomalies during spring are related to a sea surface temperature (SST) pattern that resembles the corresponding El Nino–Southern Oscillation (ENSO) SST pattern. The corresponding atmospheric circulation pattern favors enhanced moisture advection over the Rhine catchment area during positive streamflow anomalies. During autumn, the streamflow variability follows a distribution similar to spring streamflow, but with a strong peak in the 30–60-yr band. Autumn streamflow anomalie...