Climate fluctuations in the North Atlantic Ocean have wide-spread implications for Europe, Africa, and the Americas. This study assesses the relative contribution of the long-term trend and variability of North Atlantic warming using EOF analysis of deep-ocean and near-surface observations. Our analysis demonstrates that the recent warming over the North Atlantic is linked to both long-term (including anthropogenic and natural) climate change and multidecadal variability (MDV, *50-80 years). Our results suggest a general warming trend of 0.031 ± 0.006°C/decade in the upper 2,000 m North Atlantic over the last 80 years of the twentieth century, although during this time there are periods in which shortterm trends were strongly amplified by MDV. For example, MDV accounts for *60% of North Atlantic warming since 1970. The single-sign basin-scale pattern of MDV with prolonged periods of warming (cooling) in the upper ocean layer and opposite tendency in the lower layer is evident from observations. This pattern is associated with a slowdown (enhancement) of the North Atlantic thermohaline overturning circulation during negative (positive) MDV phases. In contrast, the long-term trend exhibits warming in tropical and mid-latitude North Atlantic and a pattern of cooling in regions associated with major northward heat transports, consistent with a slowdown of the North Atlantic circulation as evident from observations and confirmed by selected modeling results. This localized cooling has been masked in recent decades by warming during the positive phase of MDV. Finally, since the North Atlantic Ocean plays a crucial role in establishing and regulating the global thermohaline circulation, the multidecadal fluctuations discussed here should be considered when assessing long-term climate change and variability, both in the North Atlantic and at global scales.

Fig. 13 Schematic depicting the two states of multidecadal variability in the North Atlantic is based upon previous studies in conjunction with current findings (see Sect. 4 for details) 123

[1] The North Atlantic Oscillation (NAO) is the key indicator of long-term variability in the North Atlantic. Numerous studies have accepted as a paradigm a steady relationship between the NAO and key North Atlantic climate parameters like the sea surface temperature (SST), surface air temperature (SAT), and sea level pressure (SLP). However, some studies suggest that this relationship is not always steady. For example, the recent decline of the Arctic ice cap is accompanied by a neutral or negative NAO index, whereas the ice decline observed over the last decades is associated with the positive NAO phase and with high atmospheric cyclonicity. In this study, we point to a lack of steadiness in the relationship between the NAO and SAT, SST, and SLP over the North Atlantic region when observed over long (decadal) time intervals. This suggests that the relationship is more complex than previously thought and may require further investigation.

The Quaternary history of Beringia and of the Arctic-Pacific marine connection via the Bering Strait is poorly understood because of the fragmentary stratigraphic record from this region. We report new borehole and seismic-reflection data collected in 2006 in the southwestern Chukchi Sea. Sediment samples were analyzed for magnetic properties, grain size, heavy minerals, and biostratigraphic proxies (spores and pollen, foraminifers, ostracodes, diatoms, and aquatic palynomorphs). Two shallow boreholes drilled between the Chukotka Peninsula and the Wrangel Island recovered sediments of two principal stratigraphic units with a distinct unconformity between them. Based on predominantly reverse paleomagnetic polarity of the lower unit and pollen spectra indicative of forested coasts and climate warmer than present, the age of this unit is estimated as Pliocene to early Pleistocene (broadly between ca. 5 and 2 Ma). Attendant sedimentary environments were likely alluvial to nearshore marine. These deposits can be correlated to the seismic unit infilling valleys incised into sedimentary bedrock across much of the study area, and possibly deposited during a transgression following the opening of the Bering Strait. The upper unit from both boreholes contains Holocene 14 C ages and is clearly related to the last, postglacial transgression. Holocene sediments in Borehole 2 indicate fast deposition at the early stages of flooding (between ca. 11 and 9 ka) to very low deposition, possibly related to expansive sea ice. Closer to shore, deposition at Borehole 1 resumed much later (ca. 2 ka), likely due to a change in the pattern of coastal erosional processes and/or the demise of a landbridge between the Chukotka Peninsula and the Wrangel Island inferred from studies on mammoth distribution.

-Dinoflagellate cysts were studied in 42 samples from the surface sediments of the White Sea. The total concentration of dinocysts varies from single cysts to 25000 cyst/g of dry sediments, which reflects the biological productivity in the White Sea waters and the regional particular features of the sedimentation processes. The highest concentrations are observed in silts; they are related to the regions of propagation of the highly productive Barents Sea waters in the White Sea. Generally, the spatial distribution of dinocysts species in the surface sediments corresponds to the distribution of the major types of water masses in the White Sea. The cysts of the relatively warm-water species ( Operculodinium centrocarpum, Spiniferites sp.) of North Atlantic origin that dominate in the sediments indicate an intensive intrusion of the Barents Sea water masses to the White Sea along with hydrological dwelling conditions in the White Sea favorable for the development of these species during their vegetation period. The cold-water dinocyst assemblage ( Islandinium minutum, Polykrikos sp.) is rather strictly confined to the inner parts of shallow-water bays, firstly, those adjacent to the Onega and Severnaya Dvina river mouths.

Dating of marine sediments and faunal remains they contain in stratotype and reference sections by the methods of infrared optically stimulated luminescence (IR-OSL) of K-feldspar, optically stimulated afterglow (OSA) of quartz, electron spin resonance (ESR), and 230Th/U provides new constraints on deposition in the Yenisei mouth during the Kazantsevo interglacial. The luminescence and U–Th ages in the 120–68 ka range and 93–70 ka ESR ages show that the deposition spanned the whole marine isotope stage (MIS) 5. The sediment structures and textures, grain sizes and mineralogy, and faunal records indicate tidal and shelf deposition environments. The sampled assemblages of marine mollusks comprise taxa that typically live in relatively shallow and warm water, as well as abundant subarctic and boreal species, including the Arctica islandica index species. The variations of faunal patterns, more likely, had facies rather than climatic controls, while the sediments were deposited during transgression, in a warm climate, when the area was ice-free.

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