(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.海洋沉积物中的绝大多数氦-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）。基于缓慢沉积的远洋黏土获得的氦-3记录显示，尘埃吸积速率在百万年尺度上存在显著波动，这可能源于彗星与小行星的解体事件³。Muller与MacDonald曾提出（Muller及MacDonald，1995，doi:10.1038/377107b0），若地球轨道倾角存在此前未被认知的10万年周期，则由此引发的尘埃吸积速率周期性变化，或可解释过去百万年气候记录中该频率特征的显著性（Imbrie等，1993，doi:10.1029/93PA02751）。本文报道了海底氦-3通量的变化特征，可为该假说提供支撑。研究发现，大西洋中脊区域快速沉积的第四纪沉积物所记录的氦-3通量，以约10万年为周期发生振荡。但目前尚无法确定，10万年气候周期究竟是星际尘埃向海底输送速率周期性变化的结果、诱因，还是与之相互独立的现象。