(Table 1) Helium concentration and flux in DSDP Hole 94-607 samples

Most of the helium-3 in oceanic sediments conies from interplanetary dust particles (IDPs), and can therefore be used to infer the accretion rate of dust to the Earth through time (Ozima et al., 1984, doi:10.1038/311448a0; Takayanagi and Ozima, 1987, doi:10.1029/JB092iB12p12531; Farley, 1995, doi:10.1038/376153a0). 3He records from slowly accumulating pelagic clays indicate that the accretion rate varies considerably over millions of years, probably owing to cometary and asteroidal break-up events3. Muller and MacDonald have proposed (Muller and MacDonald, 1995, doi:10.1038/377107b0) that periodic changes in this accretion rate due to a previously unrecognized 100-kyr periodicity in the Earth's orbital inclination might account for the prominence of this frequency in climate records of the past million years (Imbrie et al., 1993, doi:10.1029/93PA02751). Here we report variations in the 3He flux to the sea floor that support this idea. We find that the flux recorded in rapidly accumulating Quaternary sediments from the Mid-Atlantic Ridge oscillates with a period of about 100 kyr. We cannot yet say, however, whether the 100-kyr climate cycle is a consequence of, a cause of, or an effect independent of these periodic changes in the rate of delivery of interplanetary dust to the sea floor.

海洋沉积物中的大部分氦-3（helium-3）源自行星际尘埃颗粒（interplanetary dust particles, IDPs），因此可用于反演地球在地质时间尺度上的尘埃吸积速率（Ozima等，1984，doi:10.1038/311448a0；Takayanagi与Ozima，1987，doi:10.1029/JB092iB12p12531；Farley，1995，doi:10.1038/376153a0）。基于沉积速率缓慢的远洋黏土得到的氦-3记录显示，尘埃吸积速率在数百万年尺度上存在显著波动，这一现象可能源于彗星与小行星的解体事件。穆勒与麦克唐纳提出假说（Muller与MacDonald，1995，doi:10.1038/377107b0）：地球轨道倾角存在此前未被认知的10万年（100-kyr）周期性，由此引发尘埃吸积速率的周期性变化，该机制或可解释过去百万年气候记录中该频率信号的显著占比（Imbrie等，1993，doi:10.1029/93PA02751）。本研究通过分析海底氦-3通量的变化特征，为该假说提供了支撑。我们发现，大西洋中脊区域第四纪快速沉积沉积物中记录的尘埃通量以约10万年为周期发生振荡。但目前尚无法确定，10万年尺度的气候周期究竟是行星际尘埃向海底输送速率周期性变化的结果、成因，还是与之独立的现象。