冲绳海槽中部28ka以来陆源物质输入和古环境演化的生源组分记录

沉积物中有机碳、生物碳酸盐和生物硅等生源组分的埋藏速率在很大程度上受到海洋古生产力的控制,常常被用作古生产力的替代指标.本文利用TOC、生物硅及CaCO3等生源组分探讨冲绳海槽中部DGKS9604孔(28°16.64'N,127°01.43'E;水深766m;柱长10.76m)距今28ka以来陆源物质输入和古环境演化对海洋生产力的影响.研究结果表明,在冬季风较强的末次冰期晚期(28～22kaB.P.),长江直接输运大量的陆源营养物质进入冲绳海槽,古生产力较高;在末次盛冰期(LGM,22～18kaB.P.),虽然河口距离海槽区更近,但大陆流域降水匮乏,河流人海径流量偏低导致海槽陆源营养物质明显减少,生产力降低,表现在生物硅和有机碳堆积速率明显降低;冰消期早期生产力与末次盛冰期相比并未明显降低,此阶段气候回暖,大陆流域降雨增加,陆源物质输入相对较高.全新世早期,古生产力快速下降,既反映海平面降低,陆源物质输入减少.还可能与冰消期寡营养盐的黑潮在海槽加强有关.DGKS9604孔CaCO3含量及堆积速率变化的总体趋势与有机碳和生物硅相反,表现为末次冰期晚期低.冰消期以来逐渐升高,一方面反映陆源物质输入的稀释作用;另一方面与黑潮加强致使钙质生物生产力增强有关.此外,15～7kaB.P.期间CaCO3含量及其堆积速率有几次明显降低,可能对应黑潮减弱、陆源冲淡水较强的环境事件.     

西菲律宾海硅藻席沉积中的多囊虫类放射虫记录及其环境意义

为了多角度理解海洋纹层沉积物的形成过程,利用在西菲律宾海采集到的含纹层硅藻席的XT47孔岩心样品,进行多囊虫类放射虫的组合变化与环境意义分析.研究表明XT47孔岩心上段260 cm厚硅藻席沉积中含有丰富的放射虫、丰度高于2×104个/克;中段260~460 cm出现5次放射虫丰度高峰与红粘土的交替旋回沉积;下段460~630 cm红粘土沉积层中放射虫稀少.依据放射虫地层种的初现生物事件,470 cm以深的年龄大于0.34 Ma,表明西菲律宾海硅藻质沉积形成于中更新世以来.此外,受暖水影响控制的Tetrapyle group和Didymocyrtis tetrathalamus tetrathalamus相对丰度在末次冰盛期（LGM）呈现显著的低值期,推测在LGM期西菲律宾海北赤道暖流的影响强度是变弱的.值得注意的是,多囊虫类放射虫的丰度与生物硅含量的变化趋势出现明显的不同步现象,推测4次生物硅含量高峰是由大型硅藻（盘筛藻）的急剧增加导致的,即西菲律宾海LGM期盘筛藻的勃发呈现明显的阶段性强弱变化;进一步发现盘筛藻的4次勃发强盛期对应着胶体虫相对丰度变化的低谷期和中深层冷水种相对丰度变化的高峰期,前者指示上层水体成层化减弱、后者指示中深层水体中营养物增多.据此,认为西菲律宾海LGM期盘筛藻勃发的4次强盛期是由于上层水体成层化减弱、下层水体中丰富的营养物上涌引起.研究结果可为菲律宾海盘筛藻勃发在LGM长时间持续并最终在海底形成厚达近3 m的硅藻席沉积提供了一种可能的解释.      

澳大利亚大堡礁海域近15万年沉积记录及古气候演化

对IODP325航次M0058A沉积岩心柱的矿物学和地球化学特征进行了详细研究,并将其与南极Vostok冰心各古气候阶段进行对比。结果表明,澳大利亚大堡礁海域海平面变化对南极冰盖增加或消融变化响应敏感。末次冰期发生之前为暖期,即Vostok冰心G阶段(140~116ka BP),冰川融化,海平面较高。沉积物红度增高,说明该时期大堡礁海域及沿岸温度较高,降雨量及其导致的入海径流较大,随之入海的石英等矿物也增多,形成较低的碳酸盐/石英含量比值;随着全球气候进入末次冰期(对应于Vostok冰心F、E、D、C和B阶段),尽管也有冷暖变化,但整体上,大堡礁海域海平面较低。在F和E阶段(116~73ka BP),沉积物红度较低,陆源输入较少,大堡礁海域海洋古生产力较低,导致沉积物有机质含量较低;在D阶段(73~58ka BP),大堡礁海域沿岸为冷干期,海平面也较低,该时期M0058A沉积岩心主要由砂构成;在C阶段(58~30ka BP),大堡礁海域降雨转多、气候较为湿润,但碳酸盐/石英含量比值较低,陆源输入物质较多,或导致了较高的海洋古生产力,从而形成沉积物高有机碳含量;在B阶段(30~13ka BP),沉积物红度较高,陆源的营养物质较多,导致总有机碳水平较高。但大量的陆源砂质物质输入,导致了碳酸盐/石英比值较低;在A阶段,末次冰期结束,全球进入末次冰后期,气温逐渐增高,冰川融化,降水增多,海平面增高,陆源营养物质增多,导致沉积红度增高、有机质含量增加。同时海平面增高,大堡礁海域水深增加,岩心M0058A所在的位置远离海岸,水动力水平较低,利于碳酸盐沉淀、不利于石英等陆源物质运移,导致该处的碳酸盐/石英比值增高。上述研究结果为全面评价末次冰期以来大堡礁海域气候环境变化提供了数据基础。     

东北印度洋区BAR9427岩心末次冰期以来的古季风活动记录

末次冰期旋回尤其是氧同位素3期气候明显不稳定, 南亚季风活动并不遵循冰期间冰期的规律.通过东北印度洋区位于安达曼海南部、苏门答腊岛西北端格雷特海峡的BAR9427岩心的古海洋学研究, 并与相邻孟加拉湾地区的MD77181和MD81349二支岩心进行对比分析, 认识到末次冰期氧同位素2期时, 研究区东北冬季风增强, 上升流活跃, 古生产力较高, 同时近岸地区蒸发作用强烈, 海水盐度升高.末次冰期大间冰阶氧同位素3期的早、晚期, 研究区西南夏季风活动强烈, 向东的西南季风流, 使得孟加拉湾中部盐度升高, 而北部由于季风降雨, 大量的淡水输入使得盐度大幅度下降, 且八月盐度远低于二月.西南夏季风变化遵循23ka的岁差周期, 在我国青藏高原、黄土与沙漠以及阿拉伯海等区都有表现.      

季风的发展与冰川的消失——从台湾高山末次冰期冰川发育特征说起

台湾高山有无第四纪冰川之争,经历60a后终于得到澄清．此次查明台湾雪山主峰区有3套 不同时期的冰川遗迹．如冰斗湖、冰坎、大型磨光面和擦痕以及冰碛垄等,分别命名为山庄冰阶(末 次冰期早期．44.25±3.72ka BP)、黑森林冰阶(末次冰期最盛,18.26±1.52 ka BP)、雪山冰阶(末次冰 期晚期,10.68±0.84 ka BP)尤其以早期冰川规模大为特征．澄清了地学界近65a来的怀疑,将为 全球变化研究增添新内容．     

近33ka以来辽河口沉积环境演变与生物硅记录

沉积物岩心记录着沉积环境的演变过程,其中生物硅(BSi)记录能反映硅质生物的生产力时间和空间变化,2012年5月在下辽河平原西南缘得到了ZK2钻孔柱状样,通过对其沉积物原位密度、生物硅、碳埋藏、粒度、AMS~(14)C和OSL测年、有孔虫鉴定、孢粉鉴定,将ZK2孔的沉积环境主要划分为上三角洲平原相沉积、海洋主导的沉积、湖相沉积、河道沉积4个沉积单元,其相应的生物硅(BSiO_2)浓度分布依次为(2.85±0.23)%、(1.55±0.10)%、(1.96±0.10)%、(0.92±0.05)%,并且生物硅的波动与颗粒有机碳浓度的波动同步。特别是在17~25 cal ka BP冰期形成的湖沼沉积出现较大的颗粒无机碳(PIC)浓度的波动,推测与当时干冷气候条件下CaCO_3过饱和从湖水中沉淀析出有关。钻孔沉积物生物硅浓度记录对格陵兰冰芯~(18)O同位素值的响应存在大约300 a的滞后现象。     

近190ka BP以来菲律宾海黑潮源区的碳酸盐旋回及其控制因素

对取自西菲律宾海黑潮源区的Ph05-5和WF3岩芯进行了CaCO3和钙质超微化石研究.在利用氧同位素曲线对比和AMS14C数据进行地层划分的基础上,结合钙质超微化石的碳酸盐溶解指数和初级生产力指标,分析了晚第四纪黑潮源区碳酸盐旋回特征及其控制因素.约190ka BP以来CaCO3含量整体上都表现为冰期高、间冰期低的"太平洋型"旋回特征,但菲律宾以东海区在末次冰期(MIS 4到MIS 2期)内部又显示出间冰段含量高、冰段含量低的"大西洋型"旋回特征.碳酸盐旋回的控制因素在黑潮源区内部也有明显的差异,菲律宾以东海区以碳酸盐溶解作用为主,初级生产力起次要作用;而台湾东南部海区的主要因素则是初级生产力变化引起的钙质生物输入量的波动.菲律宾以东海区末次冰期内部表现出的"大西洋型"旋回特征则是溶解作用和初级生产力共同影响的结果.     

生物硅早期成岩作用研究进展

硅质浮游生物是海洋初级生产力的主要提供者,其死亡后所产生的硅质残骸(生物硅)向海底的传输,是保持海洋硅循环动态平衡的重要环节。由于海洋沉积物中的硅质微体生物化石记录了古海洋初级生产力的变化及其时空分布,因而生物硅也成为古环境重建的重要替代指标。本文对生物硅在水柱沉降和表层沉积物埋藏过程中所发生的早期成岩转变及其主要影响因素进行了综述,为全面了解最近几十年来该领域的研究进展提供参考。     

西菲律宾海190ka以来钙质超微化石的氧碳同位素记录

对西菲律宾海Ph05-5柱状样190ka以来钙质超微化石进行了氧碳同位素分析.研究结果表明, 钙质超微化石δ18O值在末次间冰期(MIS 5e) 和全新世明显低于末次冰期(MIS5d~2) 和倒数第二次冰期(MIS6).超微化石δ18O值与浮游和底栖有孔虫δ18O值都呈明显的正相关关系, 但超微化石δ18O平均值比浮游有孔虫Globigerinoides rubber δ18O平均值高0.431×10-3, 比Neogloboquadrina dutertrei δ18O平均值低0.410×10-3, 而这三者又远远低于底栖有孔虫Cibicides wullerstorfi的δ18O平均值.超微化石δ13C值变化阶段性特征明显, 并与该孔超微化石绝对丰度变化趋势极为相似, 二者共同反映出西菲律宾海大约从190ka到110ka的MIS6和大约MIS 5e期, 表层海水初级生产力相当稳定且显著低于其他各时期; 大约从MIS5d期开始表层初级生产力显著上升, 初级生产力的这一高值一致持续到约25ka左右的末次冰期; 在25ka以来的MIS1、2期, 表层初级生产力有所下降, 但仍高于190ka到110ka的MIS6和MIS 5e期.      

北极楚科奇海沉积生物硅的分布及其硅质泵过程初探

依托第3次、第4次、第5次北极科学考察在北极楚科奇海采集的表层沉积物样品,通过碱液连续提取法对生物硅含量进行分析,以探讨楚科奇海的生物硅分布及硅质泵过程。结果显示,楚科奇海表层沉积物中生物硅的含量为1.23%~10.60%。高值区位于楚科奇海陆坡处72°N附近和楚科奇海南部阿纳德尔流和西伯利亚沿岸流的交界处68°N附近,低值区位于楚科奇海东部阿拉斯加沿岸流影响区域,其生物硅含量小于3%。楚科奇海表层沉积物中生物硅的分布与上层水体的初级生产力的分布格局较一致,而影响上层水体浮游植物生产的两个重要因素分别为楚科奇海环流格局(尤其是太平洋入流水的影响)和海冰融化。生物硅和有机碳之间存在很好的正相关关系,表层沉积物中蛋白石/有机碳(Sibio/Corg)的比值为1.6~2.02,与北太平洋中该比例相当,表明上层海洋硅质泵过程对楚科奇海碳埋藏的贡献较大,使得楚科奇海成为全球海洋吸收大气CO2重要的汇之一。     

末次冰消期以来赛里木湖沉积记录的气候突变

末次冰消期以来的气候突变事件的时空变化特征及其区域响应是古气候环境变化研究的重要内容,然而亚洲中部干旱区末次冰消期以来的气候突变记录较少,尤其缺少末次冰消期期间快速转暖过程的区域响应.本研究通过对位于亚洲中部干旱区的新疆西天山中部亚高山湖泊赛里木湖湖心采得的长300 cm的SLM2009钻孔沉积物的碳酸盐含量和粒度变化特征的分析,在 14 个 AMS 14C测年数据的基础上,探讨了末次冰消期约23. 4 cal. ka B. P.以来亚洲中部干旱区的气候突变事件记录及其区域响应过程.结果表明:赛里木湖湖心钻孔沉积物完整记录了 H1 ( 17. 5 ~ 15. 2 cal. ka B. P.)、 YD ( 12. 6 ~ 11. 7 cal. ka B. P.)冷事件以及 B-A ( 15. 2 ~12. 9 cal. ka B. P.)暖事件等末次冰消期气候突变事件以及全新世以来的10. 5 ka、 8. 2 ka、 5. 5 ka、 4. 2 ka、 2. 8 ka和小冰期冷事件,这与亚洲中部干旱区已有的气候突变事件记录相吻合,表明末次冰消期以来亚洲中部干旱区具有相似的气候突变演化模式.同时这些气候突变事件与高纬冰芯以及低纬石笋氧同位素记录的一致性则表明气候突变具有全球性影响,受相同的成因机制因素控制.     

Quantitative parameters of Pleistocene pelagic sedimentation in the Atlantic Ocean

Lithological–facies maps of Eopleistocene and Neopleistocene sediments (with 10 and 20 m isopachs) are compiled for the pelagic part of the Atlantic Ocean based on materials recovered by 283 ocean drilling sites. Data for both maps were calculated using A.B. Ronov’s volumetric method. The calculated results include such quantitative sedimentation parameters of major sediment types as the areas covered by these sediments, their volumes, masses of the dry sedimentary material, and masses of sedimentary material deposited per specified time unit. These parameters are compared for both Eopleistocene and Neopleistocene time, and the data are utilized to separately interpret the results for terrigenous, carbonate, and siliceous sediments. The supply of terrigenous material is proved to have been enhanced in the Pleistocene as a result of both tectonic uplift of continents and climatic changes, including intensification of continental glaciation at high latitudes in both hemispheres. The growth in the productivity of carbonate plankton was overridden by growing generation of bottom and deep water masses and ensuing intensification of the dissolution of pelagic carbonates. The productivity of siliceous plankton practically did not change, perhaps, because of a favorable combination of the supply of dissolved silica and other nutrients from both West and East Antarctica.     

Record of carbonate preservation and the Mid‐Brunhes climatic shift from a seamount top with low sedimentation rates in the Central Indian Basin

In the present investigation, an age model of carbonate‐rich cores from a seamount top in the Central Indian Basin (CIB) was constructed using both isotopic (²³⁰Th_excess, AMS ¹⁴C, oxygen isotopes) and biostratigraphic methods. The chronologies using the two methods are in good agreement, yielding a record of the late Middle Pleistocene to the Pleistocene–Holocene transition (550 to 11.5 ka). The first appearance datum (FAD) of the radiolarian Buccinosphaera invaginata (180 ka) and coccolith Emiliania huxleyi (268 ka) and the last appearance datum (LAD) of the radiolarian Stylatractus universus (425 ka) were used. A monsoon‐induced productivity increase was inferred from carbonate, organic carbon and δ¹³C records in response to the Mid‐Brunhes Climatic Shift (MBCS), consistent with an increased global productivity. While the coccolith diversity increased, a decrease in coccolith productivity was found during the MBCS. At nearly the same time period, earlier records from the equatorial Indian Ocean, western Indian Ocean and eastern Africa have shown an increased productivity in response to the influence of westerlies and increased monsoon. The influence of easterlies from Australia and the intensification of aridity are evidenced by increased kaolinite content and clay‐sized sediments in response to the MBCS. An increased abundance of Globorotalia menardii and other resistant species beginning from marine isotope stage (MIS) 11 and the proliferation of coccolith Gephyrocapsa spp. indicate increased dissolution, which is consistent with the widespread global carbonate dissolution during this period. The relatively high carbonate dissolution during the transition period of MIS 3/2 and glacial to interglacial periods (MIS 6, 7 and 8) may be due to the enhanced flow of corrosive Antarctic Bottom Water (AABW) into the CIB.     

Biological productivity, terrigenous influence and noncrustal elements supply to the Central Indian Ocean Basin: Paleoceanography during the past ∼ 1 Ma

A 2m-long sediment core from the siliceous ooze domain in the Central Indian Ocean Basin (CIOB; 13‡03′S: 74‡44′E; water depth 5099m) is studied for calcium carbonate, total organic carbon, total nitrogen, biogenic opal, major and few trace elements (Al, Ti, Fe, K, Mg, Zr, Sc,V, Mn, Cu, Ni, Zn, Co, and Ba) to understand the productivity and intensity of terrigenous supply. The age model of the sediment core is based on U-Th dating, occurrence of Youngest Toba Tuff of ∼ 74 ka and Australasian microtektites of ∼ 770 ka. Low carbonate content (< 1%) of sediment core indicates deposition below the carbonate compensation depth. Organic carbon content is also very low, almost uniform (mean 0.2 wt%) and is of marine origin. This suggests a well-oxygenated bottom water environment during the past ∼ 1100ka. Our data suggest that during ∼ 1100 ka and ∼ 400 ka siliceous productivity was lower, complimented by higher supply of terrigenous material mostly derived from the metasedimentary rocks of High Himalayan crystalline. However, during the last ∼ 400 ka, siliceous productivity increased with substantial reduction in the terrigenous sediment supply. The results suggest that intensity of Himalayan weathering, erosion associated with monsoons was comparatively higher prior to 400 ka. Manganese, Ba, Cu, Ni, Zn, and Co have around 90% of their supply from noncrustal (excess) source and their burial to seafloor remained unaffected throughout the past ∼ 1100 ka.     

Planktonic foraminifers in the southern Bering Sea: Changes in composition and productivity during the Late Pleistocene-Holocene

Taxonomic composition and distribution of planktonic foraminifers are studied in section of Core GC-11 that penetrated through Upper Quaternary sediments of the Bowers Ridge western slope, the southern Bering Sea. As is shown, structure of foraminiferal assemblage and productivity have varied substantially during the last 32000 calendar years in response to changes in surface water temperatures and water mass circulation in the northern part of the Pacific, the Bering Sea included. The productivity was maximal during deglaciation epoch, being notably lower in the Holocene and minimal at the glaciation time.     

Stable Isotope and Lithologic Evidence of Late-Glacial and Holocene Oceanography of the Northwestern Pacific and Its Marginal Seas

Stable isotopes, geochemical, lithological, and micropaleontological results from cores from the far northwest (FNW) Pacific and the Okhotsk and Bering seas are used to reconstruct the regional environment for the last glaciation, the deglacial transition, and the Holocene. δ¹⁸O records of planktonic foraminifera of the region show two “light” shifts during deglacial time, provoked by the freshening of the surface water and climate warming. These north Pacific terminal events (T1ANP and T1BNP) with ages of 12,500 and 9300 yr B.P., respectively, occur almost simultaneously with two episodes of accelerated glacier melting around the North Atlantic. Along with the isotopic shifts, the CaCO₃content in regional sediments increased abruptly (1A and 1B carbonate peaks), probably due to changes of productivity and pore water chemistry of surface sediments. Organic matter and opal concentration increased during the transition (between T1ANP and T1BNP events) in the sediments of the FNW Pacific and the southern part of the Bering Sea and opal content increased in the Holocene in the Bering and Okhotsk Seas. δ¹³C records of cores from the Okhotsk and Bering seas and the FNW Pacific do not contradict the hypothesis of increased intermediate water formation in the region during glaciation. During deglaciation, accumulation of the coarse terrigenous component decreased in sediments of the Bering Sea and the FNW Pacific before the T1ANP event, probably as a result of rising sea level and opening of the Bering Strait.     

四川茂县较场湖相沉积磁性地层初步研究

四川茂县较场剖面厚101.1m,其中湖相沉积厚98.0m,为一套浅黄色-灰色的粉砂、粘土质粉砂和粉砂质粘土层。古地磁测试显示,除2个样品的磁偏角显示负极性外,其余样品的磁偏角全部为正,属布容正极性时,没有出现B/M界线。根据该套地层的岩性、岩相和所处的地貌部位,可以和云南金沙江谷地的龙街组对比,推测其开始沉积的时代为100~120 kaBP.另外,距顶4.0 m处光释光年龄为16.7±1.2 kaBP,推测其结束于10kaBP.湖相沉积历时约100kaBP,是岷江流域出露的末次(间)冰期以来厚度最大的剖面之一。      

抚仙湖全新世自生碳酸盐及其区域气候和湖泊水位指示意义

抚仙湖是我国面积、蓄水量最大的高原湖泊之一。通过对抚仙湖FXH-B2钻孔岩芯296 cm沉积物的矿物组成和碳酸盐含量分析,结合岩芯XRF扫描数据和AMS^14C年代的测定,探讨了抚仙湖湖泊沉积物中碳酸盐含量与方解石矿物及沉积物Ca元素相对含量之间的关系及其环境指示意义,在对比和参考水下地形测量、地球物理勘探、水质和地球化学监测和不同部位钻孔岩芯的分析结果的基础上,重建了抚仙湖全新世以来气候和湖泊水位的变化。结果指示,抚仙湖碳酸盐含量与方解石的XRD信号强度、沉积物Ca元素的XRF扫描数据之间存在很高的相关性,沉积物中碳酸盐类物质主要为方解石(其他碳酸盐类矿物相对含量极微甚至可以忽略不计),沉积物中Ca元素主要来自碳酸盐,因此其含量由碳酸盐、即方解石矿物含量决定。沉积物中碳酸盐含量的变化可以用沉积物中Ca元素XRF扫描结果进行表示。由于抚仙湖处于亚热带季风气候区,以10月至次年4月降水量极少而蒸发强烈为特点的干季和以5月至9月降水为主的湿季所形成的干湿变化控制了湖泊演化的主要过程,区域气候变化是湖泊演化和水位变化的主要动力。结合湖泊沉积碳酸盐稳定同位素δ^18O和δ^13C、有机质含量及其同位素δ^13C、抚仙湖北部边缘水下侵蚀地形测量、地球物理勘探和沉积地层年代的确定和讨论,明确了抚仙湖沉积碳酸盐含量指示湖泊水位的变化,并重建了抚仙湖过去约12 ka以来水位变化的历史。结果显示,在约12 cal.ka B.P.至2.2 cal.ka B.P.期间的湖泊水位变化主要经历了波动式降低的过程,其中4.37~2.2 cal.ka B.P.期间高CaCO3含量、偏正的碳酸盐δ^18O、δ^13C值指示抚仙湖一度出现低于现代湖面约30 m左右的低水位,可能记录了抚仙湖流域极端的干旱时期,在2.2~2.0 cal.ka B.P.期间抚仙湖水位经历了快速升高的变化事件,期间湖水位快速上升达到现代湖水水位,揭示了印度季风控制区区域降水的特殊性和气候变化的突发性。     

Exploring controls of the early and stepped deglaciation on the western margin of the British Irish Ice Sheet

New optically stimulated luminescence dating and Bayesian models integrating all legacy and BRITICE-CHRONO geochronology facilitated exploration of the controls on the deglaciation of two former sectors of the British–Irish Ice Sheet, the Donegal Bay (DBIS) and Malin Sea ice-streams (MSIS). Shelf-edge glaciation occurred ~27 ka, before the global Last Glacial Maximum, and shelf-wide retreat began 26–26.5 ka at a rate of ~18.7–20.7 m a^–1. MSIS grounding zone wedges and DBIS recessional moraines show episodic retreat punctuated by prolonged still-stands. By ~23–22 ka the outer shelf (~25 000 km²) was free of grounded ice. After this time, MSIS retreat was faster (~20 m a^–1 vs. ~2–6 m a^–1 of DBIS). Separation of Irish and Scottish ice sources occurred ~20–19.5 ka, leaving an autonomous Donegal ice dome. Inner Malin shelf deglaciation followed the submarine troughs reaching the Hebridean coast ~19 ka. DBIS retreat formed the extensive complex of moraines in outer Donegal Bay at 20.5–19 ka. DBIS retreated on land by ~17–16 ka. Isolated ice caps in Scotland and Ireland persisted until ~14.5 ka. Early retreat of this marine-terminating margin is best explained by local ice loading increasing water depths and promoting calving ice losses rather than by changes in global temperatures. Topographical controls governed the differences between the ice-stream retreat from mid-shelf to the coast.