Marine Micropaleontology 121 (2015) 52–69 Contents lists available at ScienceDirect Marine Micropaleontology journal homepage: www.elsevier.com/locate/marmicro Variations of Okhotsk Sea oxygen minimum zone: Comparison of foraminiferal and sedimentological records for latest MIS 12–11c and latest MIS 2–1 Natalia Bubenshchikova a,⁎,DirkNürnbergb,RalfTiedemannc a P.P. Shirshov Institute of Oceanology, Nakhimovski pr. 36, Moscow 117997, Russia b GEOMAR, Helmholtz-Zentrum für Ozeanforschung Kiel, Wischhofstr. 1–3, D-24148 Kiel, Germany c Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Am Alten Hafen 26, D-27568, Bremerhaven, Germany article info abstract Article history: Benthic foraminiferal assemblage compositions, foraminiferal and sedimentological proxies were analyzed in Received 9 October 2014 core MD01-2415 from the northern slope of the Okhotsk Sea to compare variations of productivity and oxygen Received in revised form 21 September 2015 minimum zone (OMZ) intensity during the latest marine isotope stage (MIS) 12–11c and latest MIS 2–1. The ben- Accepted 30 September 2015 thic assemblages reveal close similarity between the two climatic cycles. The absence of benthic assemblages Available online 8 October 2015 during the latest MIS 12 and the presence of the low-productivity Angulogerina angulosa assemblage during the latest MIS 2 suggest the disappearance of the OMZ. This regime was related to almost perennial ice cover Keywords: Benthic foraminifera with periods of active ice rafting during the latest MIS 12, while it was attributed to prolonged seasonal ice Organic matter flux cover, low surface productivity and enhanced formation of well-oxygenated water masses in the Okhotsk Sea Oxygen minimum zone during the latest MIS 2. In deglacial times, the OMZ gradually intensified, as evidenced by the high- Downslope supply productivity Uvigerina akitaensis assemblage during the early termination (T) TV and early TI and the low Carbonate dissolution events oxygen-tolerant Bolivina spissa assemblage during the late TV and late TI. The orbitally forced similar rises of Okhotsk Sea the global sea level during TV and TI caused a large offshore supply of organic matter. Synchronously, nutrients from the melting sea ice and shelf erosion promoted high surface (mainly carbonate) productivity. As a result, a high and sustained flux of particulate, degraded and refractory organic matter enhanced oxygen consumption in bottom waters and sediments, leading to the similar gradual OMZ intensifications. The B. spissa assemblage also points to expansion of oxygen-depleted water mass from the North Pacific into the Okhotsk Sea, fostering the OMZ intensifications. The phytodetritus-related Islandiella norcrossi assemblage indicates weakening of the OMZ during full interglacial times of MIS 11c and MIS 1. After stabilization of the global sea level, nutrients were mainly delivered by regional upwelling and fluvial discharge, favoring increased biogenic opal and carbon- ate production in the surface water, similar to the present. In this way, moderate to high (although less than deglacial) and pulsed flux of predominantly particulate organic matter caused the weakening of the oxygen con- sumption and OMZ. Notably, during MIS 11c, the benthic assemblage with the dominance of the taxa with dissolution-resistant tests, such as Miliammina herzensteini, Karreriella baccata and Martinottiella communis,re- flects carbonate dissolution events in sediments. These events might have been resulted from an interruption of the local surface carbonate production and inflow of more carbonate-corrosive water masses from the North Pacific driven by a drawdown of the global ocean carbonate saturation. © 2015 Elsevier B.V. All rights reserved. 1. Introduction large amount of nutrients introduced by seasonal sea ice melting, fluvial discharge and local upwelling. The presence of an oxygen minimum Variations in the Okhotsk Sea primary production and formation of zone (OMZ) at low intermediate depths in the Okhotsk Sea reflects intermediate water influence global climate via the contribution to at- the balance of the high primary production and ventilation controlled mospheric CO2 concentrations and ventilation of the intermediate by both the outflow of recently-formed oxygenated Okhotsk Sea Inter- North Pacific. The paleoreconstructions of the Okhotsk Sea environ- mediate Water (OSIW) and the inflow of old oxygen-depleted Deep Pa- ments help to understand global climate change. At present, the ex- cific Water (DPW) from the North Pacific(Fig. 1). tremely high primary production of the Okhotsk Sea is favored by the Recent studies provide evidence for significant glacial to interglacial variations of the Okhotsk Sea seasonal ice cover, terrestrial organic mat- fl ⁎ Corresponding author. ter in ow, marine productivity and circulation (Gorbarenko et al., E-mail address: [email protected] (N. Bubenshchikova). 2002a; Gorbarenko et al., 2010; Iwasaki et al., 2012; Nürnberg and http://dx.doi.org/10.1016/j.marmicro.2015.09.004 0377-8398/© 2015 Elsevier B.V. All rights reserved. N. Bubenshchikova et al. / Marine Micropaleontology 121 (2015) 52–69 53 Fig. 1. A) Bathymetric chart of the Okhotsk Sea and location of core MD01-2415 (red star). Reference hydrological stations (open circle) and cores (black circles) are shown (for detailed information see Table S4 and Figures S1 and S2 of the Appendix). Solid line indicates mean sea ice extent in March during 1971–1991 (Rostov et al., 2001). B) Inset in the upper left corner shows general surface circulation pattern in the Okhotsk Sea and northwest Pacific. C) Inset in the low right corner shows dissolved oxygen (ml l−1) within the oxygen minimum zone at ~750–1500 m water depths (Bruyevich et al., 1960). The formation process of Okhotsk Sea Intermediate Water (OSIW) by: i) mixing of Dense Shelf Water (DSW) and North Pacific Water (NPW), ii) mixing driven by the inflowing dense Soya Water (SW), and iii) tidal mixing around the Kurile Straits (Freeland et al., 1998; Gladyshev et al., 2003; Moroshkin, 1966; Talley, 1991) is indicated. DPW = Deep Pacific Water, NPIW = North Pacific Intermediate Water. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Tiedemann, 2004; Seki et al., 2004; Seki et al., 2009; Seki et al., 2012). In MIS 11, and particularly MIS 11c, is considered a potential analog for particular, benthic foraminifera-based studies suggest increased pro- the present interglacial (MIS 1 or Holocene) and future climate, because ductivity, enhanced inflow of Old Pacific Water (DPW here) and weak- of the similarity in the orbital configuration (Loutre and Berger, 2003). ened outflow of the OSIW during interglacial marine isotope stage The global sea level rise during MIS 12/11 transition is seen as the youn- (MIS) 1, 5e and 9 compared to glacial MIS 2–5d, 6–8 and 10 (Barash gest analog for the sea level rise during MIS 2/1 transition, although dur- et al., 2001, Barash et al., 2006; Khusid et al., 2005). In high-resolution ing MIS 11c, the sea level stood 13 to 20 m above the present level sediment cores throughout the Okhotsk Sea, benthic foraminiferal as- (Fig. 2c) (Miller et al., 2005). To date, detailed variations of environmen- semblages dominated by bolivinids were found during termination tal conditions during MIS 11c in the Subarctic Pacific and surrounding (T) I, pointing to increased productivity, reduced oxygenation of bottom landmass are insufficiently studied because of a lack of appropriate sed- waters and intensification of the OMZ (Bubenshchikova et al., 2010; iment material. Recent pollen-based reconstructions for Lake Baikal and Gorbarenko et al., 2002a, Gorbarenko et al., 2010). Geochemical and Lake Elgygytgyn sediments indicate warmer and wetter climate condi- mineralogical studies assume the existence of anoxic bottom water con- tions over Siberia during MIS 11c as compared to MIS 1 (Melles et al., ditions in the Derugin Basin during TI (Derkachev et al., 2007)and 2012; Prokopenko et al., 2010). In the Okhotsk Sea, the available sedi- deglacial–early interglacial intervals of MIS 1, 5, 9 and 11 (Liu et al., mentological and geochemical data (including those for core MD01- 2006). To summarize, previous results suggest a basin-wide intensifica- 2415 under study) show that TV and TI and subsequent interglacials tion of the OMZ at low intermediate depths in the Okhotsk Sea during TI. of MIS 11c and MIS 1 were characterized by high productivity (Fig. 2a) Variations of the OMZ intensity during previous deglacial to interglacial (Iwasaki et al., 2012; Nürnberg and Tiedemann, 2004) and anoxic bot- intervals, however, remain largely unknown. tom water conditions in the Derugin Basin (Liu et al., 2006). Here, we 54 N. Bubenshchikova et al. / Marine Micropaleontology 121 (2015) 52–69 Fig. 2. a) The 46.23 m-long sedimentary color b* record of core MD01-2415 covering the last 1.1 million years (Nürnberg and Tiedemann, 2004), b) LR04 δ18Orecord(Lisiecki and Raymo, 2005), c) global sea level curve (Miller et al., 2005). Stratigraphical framework of core MD01-2415 (Nürnberg and Tiedemann, 2004) and the intervals under study are indicated. MIS = Marine Isotope Stage. present the first high-resolution study for the Okhotsk Sea focusing on intensity in the Okhotsk Sea during the latest MIS 12–11c and latest similarity and differences between the latest MIS 12–11c and latest MIS 2–1 and to discuss climate forcing of the regional environmental MIS 2–1 intervals, including potentially analogous interglacials over changes. late Quaternary time. This study applies mainly benthic foraminiferal assemblage compo- 2. Core location and modern oceanographic setting sition, which is a useful tool for reconstructing productivity and OMZ in- tensity in the past (Kaiho, 1994; Cannariato and Kennett, 1999; McKay The CALYPSO giant piston core MD01-2415 was recovered from the et al., 2005; Shibahara et al., 2007; Bubenshchikova et al., 2010;review northern slope of the Okhotsk Sea at 53°57.09′N, 149°57.52′E at 822 m in Jorissen et al., 2007).