Abstract:SignificanceThe North Pacific hosts extensive oxygen minimum zones. Ventilation of North Pacific Intermediate Water mitigates hypoxia in thermocline waters not under influence of ocean–atmosphere processes. Instrumental datasets show recent decadal decreases in O2, but millennial-scale natural variations in mesopelagic ventilation might be large and are not understood well. We reconstruct Holocene ventilation changes in a key region (Okhotsk Sea). Modern ventilation and O2 levels are a relatively recent featur… Show more
“…In this particular scenario, we see an AMOC overshoot, also seen during the Bølling/Allerød. At millennial scales, paleoceanographic evidences have characterized abrupt changes in the other regions as well, for example, the subpolar North Pacific Ocean (Gong et al, 2019; Lembke‐Jene et al, 2018; Lohmann et al, 2019; Maier et al, 2018; Rae et al, 2014). Such rapid shifts affect processes like surface stratification, formation and dynamics of sea ice, feedbacks with atmospheric patterns like the Aleutian Low, as well as deep and intermediate water formation across time scales.…”
The past provides evidence of abrupt climate shifts and changes in the frequency of climate and weather extremes. We explore the nonlinear response to orbital forcing and then consider climate millennial variability down to daily weather events. Orbital changes are translated into regional responses in temperature, where the precessional response is related to nonlinearities and seasonal biases in the system. We question regularities found in climate events by analyzing the distribution of interevent waiting times. Periodicities of about 900 and 1,150 yr are found in ice cores besides the prominent 1,500 yr cycle. However, the variability remains indistinguishable from a random process, suggesting that centennial-to-millennial variability is stochastic in nature. New numerical techniques are developed allowing for a high resolution in the dynamically relevant regions like coasts, major upwelling regions, and high latitudes. Using this model, we find a strong sensitivity of the Atlantic meridional overturning circulation depending on where the deglacial meltwater is injected into. Meltwater into the Mississippi and near Labrador hardly affect the large-scale ocean circulation, whereas subpolar hosing mimicking icebergs yields a quasi shutdown. The same multiscale approach is applied to radiocarbon simulations enabling a dynamical interpretation of marine sediment cores. Finally, abrupt climate events also have counterparts in the recent climate records, revealing a close link between climate variability, the statistics of North Atlantic weather patterns, and extreme events. Plain Language Summary Predicting the future spread of possible climates, the risk of climate extremes and the risk of rapid transitions is of high socioeconomic relevance. The past provides evidence of abrupt climate change and the frequency of extremes. This allows to separate anthropogenic signals from natural climate variability. Earth system models applied both to past and future scenarios will enhance our ability to detect regime shifts which are necessary to potentially predict climate extremes and transitions. We consider the response of the system to regular orbital forcing and then focus on shorter time scales down to weather. The appearance of precession is linked to nonlinear responses of the climate system to external orbital forcing. Furthermore, we find that centennial-to-millennial variability is stochastic in nature. We also discuss recent developments of climate models with superior resolution in typical retrieval regions of paleoclimate records, such as continental margins and coasts. Using this model, we find a strong sensitivity of the Atlantic meridional overturning circulation depending on where the deglacial meltwater is injected into. Meltwater into the Mississippi and near Labrador hardly affect the large-scale ocean circulation, whereas subpolar hosing related to icebergs yields a quasi shutdown. Our multiscale approach is applied to radiocarbon simulations enabling a dynamical interpretation of marine sediment cores....
“…In this particular scenario, we see an AMOC overshoot, also seen during the Bølling/Allerød. At millennial scales, paleoceanographic evidences have characterized abrupt changes in the other regions as well, for example, the subpolar North Pacific Ocean (Gong et al, 2019; Lembke‐Jene et al, 2018; Lohmann et al, 2019; Maier et al, 2018; Rae et al, 2014). Such rapid shifts affect processes like surface stratification, formation and dynamics of sea ice, feedbacks with atmospheric patterns like the Aleutian Low, as well as deep and intermediate water formation across time scales.…”
The past provides evidence of abrupt climate shifts and changes in the frequency of climate and weather extremes. We explore the nonlinear response to orbital forcing and then consider climate millennial variability down to daily weather events. Orbital changes are translated into regional responses in temperature, where the precessional response is related to nonlinearities and seasonal biases in the system. We question regularities found in climate events by analyzing the distribution of interevent waiting times. Periodicities of about 900 and 1,150 yr are found in ice cores besides the prominent 1,500 yr cycle. However, the variability remains indistinguishable from a random process, suggesting that centennial-to-millennial variability is stochastic in nature. New numerical techniques are developed allowing for a high resolution in the dynamically relevant regions like coasts, major upwelling regions, and high latitudes. Using this model, we find a strong sensitivity of the Atlantic meridional overturning circulation depending on where the deglacial meltwater is injected into. Meltwater into the Mississippi and near Labrador hardly affect the large-scale ocean circulation, whereas subpolar hosing mimicking icebergs yields a quasi shutdown. The same multiscale approach is applied to radiocarbon simulations enabling a dynamical interpretation of marine sediment cores. Finally, abrupt climate events also have counterparts in the recent climate records, revealing a close link between climate variability, the statistics of North Atlantic weather patterns, and extreme events. Plain Language Summary Predicting the future spread of possible climates, the risk of climate extremes and the risk of rapid transitions is of high socioeconomic relevance. The past provides evidence of abrupt climate change and the frequency of extremes. This allows to separate anthropogenic signals from natural climate variability. Earth system models applied both to past and future scenarios will enhance our ability to detect regime shifts which are necessary to potentially predict climate extremes and transitions. We consider the response of the system to regular orbital forcing and then focus on shorter time scales down to weather. The appearance of precession is linked to nonlinear responses of the climate system to external orbital forcing. Furthermore, we find that centennial-to-millennial variability is stochastic in nature. We also discuss recent developments of climate models with superior resolution in typical retrieval regions of paleoclimate records, such as continental margins and coasts. Using this model, we find a strong sensitivity of the Atlantic meridional overturning circulation depending on where the deglacial meltwater is injected into. Meltwater into the Mississippi and near Labrador hardly affect the large-scale ocean circulation, whereas subpolar hosing related to icebergs yields a quasi shutdown. Our multiscale approach is applied to radiocarbon simulations enabling a dynamical interpretation of marine sediment cores....
“…The source waters of modern NPIW are from the Okhotsk Sea, western subpolar gyre and the Gulf of Alaska (Yasuda, 1997; You et al., 2000) (Figure ), dominantly controlled by winter saline water production in these regions (Shcherbina et al., 2003; You et al., 2000). A variety of mechanisms including sea ice volume (Worne et al., 2019), closure of the Bering Strait (Kender et al., 2018; Knudson & Ravelo, 2015), strength of the East Asian summer monsoon and associated moisture and heat transports (Lembke‐jene et al., 2018), exchange of saline water between the subtropical and subpolar gyres and local net precipitation (Gong et al., 2019) have been put forward to interpret the millennial and glacial‐interglacial changes of the NPIW formation. However, how the NPIW formation responded to the atmospheric‐oceanic process and acted on the atmospheric CO 2 change on the precession scale, especially during the early interglacial, remain unclear.…”
Carbon release from the North Pacific in glacial‐interglacial cycles has been mainly linked to the North Pacific Intermediate Water (NPIW) formation and associated carbon/nutrient water upwelling and biological productivity changes. However, relationship between NPIW and atmospheric CO2 change in the early interglacial remains unclear. Here we report a high‐resolution sediment record of NPIW evolution based on paleo‐redox changes in the Western North Pacific during the last 400 ka. Our proxy and model results reveal a delayed collapse of NPIW after the glacial termination was coeval with decreased salinity of intermediate water and increased net rainfall in the North Pacific. Such weakened NPIW formation in the North Pacific probably make a contribution to maintain high atmospheric CO2 concentrations through weakened intermediate‐to‐deep ocean stratification and reduced subsurface biological pump net efficiency, countering the return to more stratified conditions in the Southern Ocean, which should drive down atmospheric CO2 during the early interglacial.
“…The fourth line of evidence is the association of centennial-scale, in-phase relations between Chl- a , SCEs, sea-ice-associated diatom species with OSIW ventilation inferred from both the sedimentary abundance of the radiolarian Cycladophora davisiana (Itaki and Ikehara, 2004) and epibenthic foraminifer δ 13 C (Lembke-Jene et al, 2018) that were reconstructed from the western Okhotsk Sea (sites GH01–1011 and LV28-4-4, respectively; Fig. 8).…”
Section: Discussionmentioning
confidence: 99%
“…Figure 8.Temporal relationship between records of productivity indices in core sample T3 and other paleoceanographic proxies. (a) Okhotsk Sea Intermediate Water (OSIW) ventilation index from off East Sakhalin (LV28-4-4, 674 m water depth; Lembke-Jene et al, 2018), (b) relative abundance of Cycladophora davisiana (G01-1011, 1348 m water depth; Itaki and Ikehara, 2004), (c) relative abundance of Coastal Oyashio-associated diatom species (percentage sum of Bacterosira bathyomphala , Fragilariopsis oceanica , and Fragilariopsis cylindrus ), (d) Chl- a (concentrations of chlorophyll a and its derivatives), (e) steryl chlorin esters (SCEs) concentrations, (f) biogenic opal concentrations (wt %: weight %), (g) relative abundance of Fragilariopsis doliolus , (h) biogenic opal concentrations (wt %: weight %) from PC6 site (Minoshima et al, 2007), (i) deposition rate of Japanese sardine scales (Kuwae et al, 2017). Blue shade denotes interval of increased abundance of Coastal Oyashio-associated diatom species.…”
Section: Discussionmentioning
confidence: 99%
“…doi: 10.5067/AQUA/MODIS/L3B/CHL/2018, accessed on 26/03/2021); (c) is enlarged map of the area in the white rectangle in (b). In (b), open circles denote coring sites T3 (piston core T3, multi-core T3 MC4-1), LV28-4-4 (Lembke-Jene et al, 2018), and PC06 (Minoshima et al, 2007); DSW: dense shelf water, ESC: Eastern Sakhalin current, OSIW: Okhotsk Sea intermediate water, CO: Coastal Oyashio, OY: Oyahio, EKC: East Kamchatka Current, WSG: Western Subarctic Gyre, K-O: Kuroshio-Oyashio transition, KR: Kuroshio, KE: Kuroshio Extension.…”
Little is known about the dynamics of marine food chains spanning primary to higher trophic levels on centennial and longer timescales, especially where the supply of dissolved iron limits primary productivity. To elucidate the long-term dynamics of biological productivity in the Coastal Oyashio (CO), which is a major pathway for transporting dissolved iron into the western North Pacific from winter to spring, we reconstructed the lower trophic level productivity over the last 3000 years in the CO. Our results demonstrate that the concentrations and mass accumulation rates of both Chl-a (chlorophyll a and its derivatives) and biogenic opal used as proxies of primary productivity, and steryl chlorin esters (SCEs) used as that of zooplankton productivity, show a millennial-scale increasing trend and centennial-scale variability beginning ca. AD 400. SCEs were positively correlated with Chl-a, indicating that changes in zooplankton productivity were induced by bottom-up control of primary productivity. The Chl-a and SCEs showed synchronous centennial-scale patterns with a relative abundance of sea-ice-associated diatom species transported by CO, and with a ventilation index in the Okhotsk Sea Intermediate Water. This synchronous pattern indicates that lower trophic-level productivity during the spring bloom responded to the intensity of iron-replete CO.
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