Hanna S. Sundqvist

Northern Hemisphere hydroclimate variability over the past twelve centuries

Accurate modelling and prediction of the local to continental-scale hydroclimate response to global warming is essential given the strong impact of hydroclimate on ecosystem functioning, crop yields, water resources, and economic security. However, uncertainty in hydroclimate projections remains large, in part due to the short length of instrumental measurements available with which to assess climate models. Here we present a spatial reconstruction of hydroclimate variability over the past twelve centuries across the Northern Hemisphere derived from a network of 196 at least millennium-long proxy records. We use this reconstruction to place recent hydrological changes and future precipitation scenarios in a long-term context of spatially resolved and temporally persistent hydroclimate patterns. We find a larger percentage of land area with relatively wetter conditions in the ninth to eleventh and the twentieth centuries, whereas drier conditions are more widespread between the twelfth and nineteenth centuries. Our reconstruction reveals that prominent seesaw patterns of alternating moisture regimes observed in instrumental data across the Mediterranean, western USA, and China have operated consistently over the past twelve centuries. Using an updated compilation of 128 temperature proxy records, we assess the relationship between the reconstructed centennial-scale Northern Hemisphere hydroclimate and temperature variability. Even though dry and wet conditions occurred over extensive areas under both warm and cold climate regimes, a statistically significant co-variability of hydroclimate and temperature is evident for particular regions. We compare the reconstructed hydroclimate anomalies with coupled atmosphere–ocean general circulation model simulations and find reasonable agreement during pre-industrial times. However, the intensification of the twentieth-century-mean hydroclimate anomalies in the simulations, as compared to previous centuries, is not supported by our new multi-proxy reconstruction. This finding suggests that much work remains before we can model hydroclimate variability accurately, and highlights the importance of using palaeoclimate data to place recent and predicted hydroclimate changes in a millennium-long context.

Corrigendum to "Climate change between the mid and late Holocene in northern high latitudes – Part 1: Survey of temperature and precipitation proxy data" published in Clim. Past, 6, 591–608, 2010

th sentence The available reconstructions indicate that the north- ern high latitudes were warmer in both summer, winter and the annual mean temperature at the mid-Holocene

Stable isotope variations in stalagmites from northwestern Sweden document climate and environmental changes during the early Holocene

This paper presents two early Holocene (9.6-5.9 ka BP) high-resolution stable isotope records of stalagmites from two caves in northwestern Sweden (Korallgrottan and Labyrintgrottan). Close similarities between the Swedish records and a previously presented Norwegian stalagmite oxygen isotope record emphasize the potential of Scandinavian stalagmites to provide high-resolution regional palaeoclimatic information. The stable oxygen isotope records are interpreted to reflect the temperature evolution during the early Holocene with a gradual warming from c. 9.6 ka BP, interrupted by cooler conditions at 8.5-8.0 ka BP. The results indicate that the cooler conditions were driven by two to three abrupt cold events rather than one ‘8.2 event’ only. Except for these cold events the stalagmite oxygen isotope records show that temperatures in northwestern Sweden were warmer than today between 9.6 and 5.9 ka BP and that during this period the interval between 7.8 and 5.9 ka BP seems to have been the warmest. The high-amplitude changes in the stable carbon isotope record of Labyrintgrottan are proposed to reflect changes in local vegetation. The area above Labyrintgrottan was most likely covered by much denser vegetation than today at the time of stalagmite growth (9.5-7.5 ka BP) and was -unlike today -probably situated below the local tree limit between 9.0 and 8.0 ka BP.

Can XRF scanning of speleothems be used as a non-destructive method to identify paleoflood events in caves?

We have developed a novel, quick and non-destructive method for tracing flood events in caves through the analysis of a stalagmite thick section with an XRF core scanner. The analyzed stalagmite ha ...

Luminescence Variations in Fast‐Growing Stalagmites from Uppsala, Sweden

Abstract Two fast‐growing stalagmites from a cellar vault in Uppsala, southeast Sweden, are analysed for their luminescent properties. The results indicate that variations in luminescence intensity in the stalagmites are annual. Due to problems in finding a suitable absolute dating method this assumption cannot yet be firmly tested; however, results from radiocarbon dating of one of the stalagmites do not contradict the proposal that the laminae are annual. If so, the speleothems have been growing for 10–15 years with a growth rate of 3–8 mm per year, which is a similar rate to other fast‐growing speleothems in Great Britain that have formed from the reaction of lime mortar and carbon dioxide. It is likely that the assumed annual laminae of the luminescence record represent a flush of organic material.

Decadal Rainfall Dipole Oscillation over Southern Africa Modulated by Variation of Austral Summer Land-Sea Contrast along the East Coast of Africa

AbstractA rainfall dipole mode characterized by negative correlation between subtropical southern Africa and equatorial eastern Africa is identified in instrumental observation data in the recent 100 years. The dipole mode shows a pronounced oscillation signal at a time scale of about 18 years. This study investigates the underlying dynamical mechanisms responsible for this dipole pattern.It is found that the southern African rainfall dipole index is highly correlated to the land–sea contrast along the east coast of Africa. When the land–sea thermal contrast strengthens, the easterly flow toward the continent becomes stronger. The stronger easterly flow, via its response to east coast topography and surface heating, leads to a low pressure circulation anomaly over land south of the maximum easterly flow anomalies and thus causes more rainfall in the south.On a decadal time scale, an ENSO-like SST pattern acts to modulate this land–sea contrast and the consequent rainfall dipole. During a “wet in the south...

Stable isotope variations in stalagmites from northwestern Sweden document changes in temperature and vegetation during the early Holocene: a reply to Hammarlund and Edwards:

In a comment on the paper by Sundqvist et al. (2007a), Hammarlund and Edwards suggest that the oxygen isotope signal of the speleothem records K1 and L4 from northwestern Sweden as well as for the earlier published stalagmite SG93 from northern Norway should mainly reflect variation in the δ 18O of mean annual precipitation. The main argument used by the authors is that the SG93 δ18O record should show remarkable similarities with the lacustrine carbonate δ18O record from Lake Tibetanus. The similarities between SG93 and Lake Tibetanus are mainly seen for the period between 10 and 9 ka BP, which is a period where both records have higher δ18O values compared with later in the Holocene. If true, this would indicate that temperatures in northern Scandinavia would have reached their Holocene maximum between 10 and 9 ka BP, which is contrary to what has been reported from other archives in the region which place the Holocene climatic optimum somewhere between 8 and 5 ka BP. Several factors affect the δ18O of speleothems and definitely also by annual mean δ18O of the local precipitation. However, for Holocene speleothems from northern Scandinavia as well as from the Alps this signal seems to be overridden by other factors, such as variable mixing of summer and winter precipitation of cave drip water as well as the temperature-dependent fractionation between calcite and water. But the relative importance of the factors can differ between different timescales, caves and even speleothems from the same cave, depending on hydrological pathways. To better understand the factors controlling the stable oxygen isotopes in precipitation and proxy archives back in time there is a need for more highly resolved records as well as for more atmospheric and hydrological modelling.