NOAA/WDS Paleoclimatology - Oro Lake, Saskatchewan 6,800 Year Salinity Reconstruction

Three high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores from the Canadian prairies, show that shifts in drought conditions have prevailed on centennial to millennial time scales for at least the past six millennia. These shifts in mean aridity exhibit broad regional synchrony, with particularly pronounced shifts at all sites between ~1700-2000 cal. yr bp and ~3600-3900 cal. yr bp, as well as at ~5400-5500 cal. yr bp for the two sites which extend back to at least 6000 cal. yr bp. The two Saskatchewan lakes exhibited significant coherence in both the timing and direction of these shifts, whereas inferred changes at the westernmost site in Alberta were significantly correlated to the Saskatchewan sites, but opposite in sign, and exhibited more high-frequency variation on the scale of centuries. The mechanisms behind these abrupt shifts in aridity are poorly understood, but may be linked to changes in oceanic-atmospheric interactions that influence the mean position of the jetstream and the associated storm tracks. Natural shifts in mean climatic conditions may accelerate with increasing carbon dioxide levels intensifying the likelihood of extreme droughts in North American prairies.

三项基于加拿大草原地区湖泊沉积物岩芯硅藻分析的高分辨率气候重建结果表明，至少在过去6000年间，干旱状况的演变始终以百年至千年尺度持续发生。这类平均干旱程度的变化呈现出广泛的区域同步特征：所有研究点位均在约1700~2000校准年BP（calendar years before present, cal. yr BP）以及3600~3900校准年BP时段出现尤为显著的干湿转变；对于至少可追溯至6000校准年BP的两处研究点位，还在约5400~5500校准年BP时段出现了显著干湿波动。两处萨斯喀彻温省湖泊的干湿转变在时间节点与变化方向上均表现出高度一致性；而阿尔伯塔省最西侧研究点位的推断干湿变化，虽与萨斯喀彻温省点位存在显著相关性，但其变化趋势恰好相反，且在百年尺度上呈现出更高频的波动。目前学界对这类干旱突变的驱动机制仍知之甚少，但推测其可能与影响急流平均位置及相关风暴路径的海-气相互作用变化有关。随着大气二氧化碳浓度升高，平均气候条件的自然转变速率可能会进一步加快，进而加剧北美草原地区极端干旱的发生风险。