31. INFRONDES is a hapax legomenon.
32. HIC FRETA VEL PEDITI PERVIA REDDIT HIEMPS. Other mentions of the sea's freezing at vii 7, Tr II 196, III x 35-50 & V x 2, and EP III i 15-16 (to the Pontus) 'tu glacie freta uincta tenes, et in aequore piscis / inclusus tecta saepe natauit aqua'.
Parts of the Black Sea do in fact freeze: 'In winter, spurs of the Siberian anticyclone (clear, dry, high-pressure air mass) create a strong current of cold air, and the northwestern Black Sea cools down considerably, with regular ice formation' (article on "Black Sea", Encyclopaedia Britannica, Macropaedia vol. 2, pp. 1096-98 [Chicago: 1974]).
32. HIEMPS. For the last one hundred years, the spelling given in editions of Latin texts has generally been hiems (some exceptions are Palmer's Heroides, the Paravia Virgil, and Reynolds' editions of Seneca), but the spelling in the ancient manuscripts of Virgil is invariably hiemps. Munro's argument for this spelling seems unanswerable: 'obeying the almost unanimous testimony of our own [i.e. O and Q of Lucretius] and other good mss. we cannot but give umerus umor and the like: also hiemps. I have heard it asked what then is the genitive of hiemps; to which the best reply perhaps would be what is the perfect of sumo or the supine of emo. The Latins wrote hiemps, as they wrote emptum sumpsi sumptum and a hundred such forms, because they disliked m and s or t to come together without the intervention of a p sound; and our mss. all attest this: tempto likewise is the only true form, which the Italians in the 15th century rejected for tento' (Lucretius ed. 4 vol. 1 p. 33).
33-34. VT, QVA REMVS ITER PVLSIS MODO FECERAT VNDIS, / SICCVS CONTEMPTA NAVE VIATOR EAT. Ovid has in mind Virgil's description of the freezing of a Scythian river (G III 360-62) 'concrescunt subitae currenti in flumine crustae, / undaque iam tergo ferratos sustinet orbis, / puppibus illa prius, patulis nunc hospita plaustris'.
35. QVI VENIVNT ISTINC VIX VOS EA CREDERE DICVNT; / QVAM MISER EST QVI FERT ASPERIORA FIDE. For Ovid's fear that his accounts of what he has undergone will not be believed, see vii 3-4 and Tr I v 49-50, III x 35-36 & IV i 65-66. In particular, see ix 85-86 'mentiar, an coeat duratus frigore Pontus, / et teneat glacies iugera multa freti'.
37-38. NEC TE CAVSAS NESCIRE SINEMVS / HORRIDA SARMATICVM CVR MARE DVRET HIEMPS. Ovid's principal explanation of the freezing of the Euxine, the low salinity of the water, is found in four other Latin authors. At IV 718-28, Valerius Flaccus offers a catalogue of rivers similar to that of Ovid, and, like Ovid, gives the cold winter winds as a subsidiary reason for the freezing. It is quite possible that Ovid is Valerius' source; but this is very unlikely to be the case for Macrobius Sat VII xii 28-38 (cited by Burman). The passage is a discussion of why, although oil congeals, wine and vinegar do not. Wine does not freeze because it contains elements of fire; this is why Homer called it αἴθοπα οἶνον. Vinegar does not freeze because it is so bitter; it is like seawater, which because of its bitterness does not congeal. 'nam quod Herodotus historiarum scriptor contra omnium ferme qui haec quaesiuerunt opinionem scripsit [IV 28], mare Bosporicum, quod et Cimmerium appellat, earumque partium mare omne, quod Scythicum dicitur, id gelu constringi et consistere, aliter est quam putatur'. It is not the seawater that freezes, but the layer of fresh water above it, which comes from the rivers that flow into the Euxine. Macrobius goes on to explain that there is an outflow of fresh water to the Mediterranean and an influx of seawater, with perfect correctness: the Encyclopaedia Britannica article cited at 32 notes that 'Flows in the Bosporus are complex, with surface Black Sea water going out and deep, saltier water coming in from the Sea of Marmara*.
There can be very little doubt, given the identity of the explanations and the similarity of language, that Ovid and Macrobius were drawing on a common source. The same source is reflected at Gellius XVII viii 8-16. Here Taurus the philosopher asks Gellius why oil often congeals, but wine does not. Gellius answers that wine is fiery by nature, which is why Homer called it αἴθοπα οἶνον. Taurus responds that wine is indeed known to have fire in it, for it warms the body when drunk; yet vinegar, in spite of its cooling effects, never freezes; perhaps things which are light and smooth are more prone to freezing. It is also worth asking why fresh water freezes, but seawater does not. 'tametsi Herodotus ... historiae scriptor contra omnium ferme qui haec quaesiuerunt opinionem scribit mare Bosporicum, quod Cimmerium appellatur, earumque partium mare omne quod Scythicum dicitur, gelu stringi et consistere'. No explanation for the freezing-over is given.[22]
Ammianus Marcellinus XXII 8 48 gives the same two explanations for the Euxine's freezing as Ovid: 'quicquid autem eiusdem Pontici sinus Aquilone caeditur et pruinis, ita perstringitur gelu ut nec amnium cursus subteruolui credantur, nec per infidum et labile solum gressus hominis possit uel iumenti firmari, quod uitium numquam mare sincerum, sed permixtum aquis amnicis temptat'. At XXII 8 46 he once again mentions the sweetness of the Euxine's waters.
Lucan describes the freezing of the Euxine (V 436-41), but gives no explanation of the cause.