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Precise agricultural statistics are necessary to track productivity and design sound agricultural policies. Yet, in settings where multi-cropping is prevalent, even crop yield—perhaps the most common productivity metric—can be challenging to measure. In a survey of the literature on crop yield in low-income settings, we find that scholars specify how they estimate the area denominator used to measure yield in under 10% of cases. Using household survey data from Tanzania, we consider four alternative methods of allocating land area on multi-cropped plots, ranging from treatment of the entire plot as the yield denominator to increasingly precise approaches that account for the space taken up by other crops. We then explore the implications of this measurement decision for analyses of yield, focusing on one staple crop that is often grown on its own (rice) and one that is frequently found on mixed plots and in intercropped arrangements (maize). A majority (64%) of cultivated plots contain more than one crop, and average yield estimates vary with different methods of calculating area planted—particularly for maize. Importantly, the choice among area methods influences which of these two crops is found to be more calorie-productive per hectare. This choice also influences the statistically significant correlates of crop yield, such that the benefits of intercropping and including legumes on a maize plot are only evident when using an area measure that accounts for mixed cropping arrangements. We conclude that the literature would benefit from greater clarity regarding how yield is measured across studies.

The Southern Hemisphere westerly winds (SWW) play a critical role in global climate, yet their behavior on decadal to centennial timescales, and the mechanisms driving these changes during the preindustrial era, remain poorly understood. We present a decadally resolved record of dust compositions using strontium and neodymium isotope ratios in mineral dust from the Siple Dome ice core, Antarctica, to explore the potential that abrupt changes in SWW behavior occurred over the past millennium. The record spans portions of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) intervals as defined in the Northern Hemisphere. We find evidence of an abrupt strengthening of atmospheric circulation during the MCA at ∼1125 CE (825 BP) that persisted for about 60 yr, indicating increased influence of Patagonia‐sourced dust. This occurs during an extended positive phase of Southern Annular Mode (SAM+)‐like conditions, characterized by high SWW velocities and a southerly shift of the main wind belt toward ∼60°S, suggesting that rapid changes in SWW strength could occur under the present SAM+ pattern. A second 20 yr long shift in dust compositions during the LIA at ∼1748 CE (200 BP) is coincident with higher dust delivery to Siple Dome, and may indicate increased dust emissions related to glacier activity in Patagonia. The new Siple Dome ice core data set demonstrates that Sr‐Nd isotopes can be used to trace shifts in atmospheric circulation on decadal timescales. The prevailing winds that encircle Antarctica, blowing west to east, play an outsized role in global climate. Because they blow continuously over the ocean, they create ocean currents and cause upwelling. When deep ocean water comes to the surface, it releases carbon dioxide into the atmosphere, causing the climate to warm. Changes in wind strength and positioning modulate the release of carbon dioxide. Therefore, knowing how and why the winds shift is important for understanding how Earth's climate system operates. We use the composition of dust preserved in an Antarctic ice core to learn how the balance of dust sources changed during the past millennium. This allows us to track past shifts in the winds around Antarctica and to learn how they respond to climate changes on short timespans, such as decades to centuries. We observe an abrupt change in dust composition at ∼1125 CE lasting for about 60 yr, indicating a greater influence of dust sourced from Patagonia in South America. This dust shift occurred during a globally observed warm period, and corresponded with an interval of stronger westerly winds blowing closer to Antarctica. Our data show that decade‐scale changes can be superimposed on longer intervals of intensified wind strength. An ice core dust provenance record from Siple Dome shows marked shifts at about 1125 CE (lasting ∼60 yr) and 1748 CE (∼20 yr)Sr‐Nd isotopes indicate changes in the relative deposition of dust from Patagonian and Antarctic sources driven by changes in windsData suggest decade‐scale changes can be superimposed on longer intervals of intensified westerly wind strength during SAM + ‐like phases An ice core dust provenance record from Siple Dome shows marked shifts at about 1125 CE (lasting ∼60 yr) and 1748 CE (∼20 yr) Sr‐Nd isotopes indicate changes in the relative deposition of dust from Patagonian and Antarctic sources driven by changes in winds Data suggest decade‐scale changes can be superimposed on longer intervals of intensified westerly wind strength during SAM + ‐like phases

In the eastern Loess Plateau region of northern China, the Quaternary loess-soil sequences of the last 2.6Ma are underlain by the Hipparion Red-Earth Formation.Magneto-stratigraphic studies suggest that it is a near continuous terrestrial record for the period from ∼7 to ∼2.6Ma BP, and therefore, has great potential for the study of Asian paleoclimates. The origin of this formation is controversial and needs further study. In this work, the Xifeng Red-Earth section, a type section for the eastern Loess Plateau region, was studied using optical microscopic analysis, grain-size measurements, and both major- and trace-element geochemical properties to address questions of its origin and environmental implications. The results show that this formation consists of three parts. The Lower part (>6.2Ma BP) is a water-reworked deposit related to alluvial and slope processes; the Middle part (from ∼6.2 to ∼3.6Ma BP) was derived from in situ eolian dust deposition, but was significantly affected by groundwater oscillations; and the Upper part (from ∼3.6 to ∼2.6Ma BP) is an eolian formation, similar to the Quaternary loess-soil sequence. The grain-size of the Upper part is significantly coarser than for the middle part, but finer than for the overlying loess.

The distribution of quartz in the surface sediments of the Atlantic Ocean reflects derivation from continents by means of rivers, wind, ice, and coastal erosion. Enrichment of quartz thus supplied has occurred in some deep basins of especially the southern high latitudes from winnowing of finegrained clays by bottom currents. Although similar modes of quartz transport may have operated both during the Holocene and the last glacial maximum (18,000 yr B.P.), significant differences in the intensity of transport and in the locii of deposition, which are attributable to climatic variations during these times, exist in some areas of the Atlantic. In Holocene sediments of the eastern equatorial Atlantic, a band of high percent quartz exists directly off the present Saharan Desert and Sahel region and reflects the trade-wind transport of dusts from these arid and semiarid regions. During the last glacial maximum (18,000 yr B.P.), this high quartz band expanded southward by about 8° of latitude. This expansion was caused not only by the southward expansion of aridity and desert dunes but also by the southward migration of the northerly belt of trade winds during the last glaciation. Relatively high abundances and accumulation rates of quartz during the last glaciation suggest higher intensities of trade winds during that time compared to the Holocene. In the North Atlantic, the abundances of quartz in Holocene sediments are high adjacent to Greenland-Iceland and in the areas off Newfoundland-Labrador, and gradually decrease toward the central areas. The polar front and limit of sea-ice melting are at present confined to the northern part of the North Atlantic. The ice-rafting of quartz grains is, therefore, effective in the areas adjacent to Greenland and to some extent off Labrador causing high abundances in these areas. In contrast to this, during the last glaciation, the quartz abundances and accumulation rates are high in the central areas of North Atlantic around 45°N and decrease toward Greenland-Newfoundland. The migration of the polar front to as far south as 45°N and the consequent southward migration of sea-ice melting and ice-rafting during the last glaciation apparently caused this change in distribution. In addition to ice-rafting at present, wave or current reworking of relict glacial-marine detritus may have caused the high abundance of quartz in the surface sediments off Newfoundland-Labrador. In 18,000 yr B.P. sediments of the Norwegian Sea, the area of high percent quartz (>10%) is more extensive than that in Holocene sediments. This reflects the greater influence of ice-rafting or glacier activity in the sediment dispersal in the Norwegian Sea during the last glacial times.

The distributions of clay minerals in the surface sediments based on about 100 new samples from the eastern Indian Ocean reveal several distinctive sediment sources which differ from those reported previously by other workers. We observe the following: (1) large zones around the periphery of the study area are characterized by abundant smectite. These largely volcanogenic sediments are derived from the Indonesian Archipelago in the northeast, from submarine volcanics of the Mid-Indian Ocean Ridge and nearby areas in the southwest, and from the Deccan Traps of India along the western side of the Bay of Bengal. The effect of Indonesian volcanism is also observed in the Cocos-Roo Rise area and on the Ninety East Ridge between 05°N and 15°S. The chief agents of transport in the case of Deccan smectite are turbidity currents and counter-clockwise surface water circulation, and, in the case of Indonesian volcanics, wind. (2) The Ganges Cone and the Java Trench are characterized by relatively more abundant illite and chlorite dispersed primarily by turbidity currents from the Ganges and Brahmaputra rivers. The influence of this sediment source extends well south of the equator on both sides of the Ninety East Ridge. The southwestern part of the Ganges Cone, is, however, characterized by smectite-rich sediments derived from the Deccan Traps. (3) A zone extending west of Australia to the Ninety East Ridge, contains relatively abundant kaolinite which is probably wind-borne from that continent. Comparison of clay mineralogy in several of these regions between Quaternary and pre-Quaternary sediments indicates changes in sediment sources and/or transport mechanisms in the geological past. For example, west of Australia, abundant volcanogenic smectite was deposited during the Cretaceous-Eocene and the relatively high kaolinite characteristics of the Quaternary sediments has been supplied only since the Miocene.

A four‐year, high‐resolution (<2 mo) record of mineralogical and isotopic (Sr and Nd) characteristics of mineral dust deposited at NorthGRIP confirms the seasonal variability in the eastern Asian source regions providing dust to northern Greenland at present. Comparison of the Sr and Nd isotopic compositions of the dust with those of potential source area samples from China and Mongolia support that the Takla Makan desert is the primary source, supplying most if not all of the mineral particles during the dusty spring season. A different source area, however, plays a role during most of year and during the low‐dust season (summer through winter) in particular. Inner Mongolian deserts of northern China, including the Tengger and the Mu Us, are likely candidates but the Mongolian Gobi is ruled out as a significant contributor to Greenland.